An atom is the smallest particle of an element that demonstrates the properties of the element and can form chemical bonds.
Some substances exist as single atoms such as metals and noble gases. Examples of metals are sodium, potassium, calcium, magnesium, copper and iron. Examples of noble gases are helium, neon and argon. Each atom can be represented by the symbol found in the Periodic Table of Elements. (see below)
An atom is frequently represented as circles of various sizes and with the chemical symbol in the middle.
Molecule
A molecule is made up of two or more atoms chemically combined together.
When the atoms are all of the same type (same element), the substance is called an element. For example, hydrogen gas, oxygen gas, nitrogen gas, fluorine, chlorine and iodine. These are all diatomic molecules, being made up of two atoms of the same type chemically combined together. Hydrogen gas is made up of two hydrogen atoms chemically combined together while fluorine is made up of two fluorine atoms combined together. See diagrams below.
When the atoms consist of different types (different elements), the substance is called a compound. For example, carbon dioxide, water, sodium chloride (table salt), sugar, ethanol and ethanoic acid (acetic acid, a major component of vinegar).
Molecular formula
Molecular formulae are used to represent the composition of molecules. It tells you how many different elements are present in the molecules, and how many atoms of each element can be found. Hence it can also tell you the total number of atoms present in a molecule.
The number of atoms for each element is written as a subscript. Take note that when the number is 1, it will not written explicitly. This means that where this is no number written beside a symbol, the number of atom is taken to be 1.
For example, H2 represents the hydrogen gas molecule and consists of two hydrogen atoms chemically combined together. H2O represents the water molecule and consists of two hydrogen atoms and one oxygen atom chemically combined together.
Another way to represent atoms and molecules is using circles of different sizes. Atoms of different elements have different sizes, colours and symbols. If you are interested to know the colours that you should use, read this Wikipedia article, https://en.wikipedia.org/wiki/CPK_coloring!
Molecular formulae are specific. Just a tiny difference in the number of atoms results in a completely different substance. For example, compare these two elements, oxygen and ozone. O2 is oxygen gas and consists of 2 oxygen atoms chemically combined and it is an important gas needed for respiration for all living things, including humans. However, O3, which is ozone and consists of 3 oxygen atoms chemically combined, is toxic to the lungs and destroys the ozone layer.
As another example, compare these two compounds, carbon monoxide CO and carbon dioxide CO2. CO (1 carbon atom and 1 oxygen atom) is a poisonous gas that prevents the red blood cells from absorbing oxygen while CO2 (1 carbon atom and 2 oxygen atoms) is a harmless gas produced as a by-product of cellular respiration.
Pros:
- Molecular formulae are simple and straightforward to read
- Molecular formulae are compact representation of molecules.
- Able to know the number and type of elements present
- Able to count the number of atoms for each element and the total number of atoms
Cons:
- Does not show the types of chemical bond that join atoms up
- Does not show how atoms are joined up
- Does not show the overall shape and size of the atoms and molecules
Properties of Substances
There are two types of properties that are used to describe substances, whether they are elements, compounds or mixtures: physical properties and chemical properties. The subsequent sections on elements and compounds will require you to describe substances in terms of their properties.
Physical properties
Physical properties are properties which can be observed or measured without any change in the chemical nature of a substance. Examples:
1. Flexibility/Elasticity
Flexibility/Elasticity is the ability of a substance to return to its original shape and size after being stretched or bent.
Wood and glass are not elastic. Rubber and some plastics are elastic.
2. Strength
Strength is the ability of a substance to withstand a heavy load without breaking or deforming.
Hardwood, ceramic and many metal alloys are strong and are used as building materials. Graphite, fibres and some plastics are weak. [use strong or weak]
3. Hardness
Hardness is the ability of a substance to withstand scratches.
Diamonds are the hardest known substance while some metals are soft enough to be cut by a knife.
Mohs scale is used by geologists to rank the hardness of substances. It ranges from 0 (the softest) to 10 (the hardest). Diamond is given 10. [use hard or soft]
4. Malleability
Malleability is the ability of a substance to be hammered or beaten into different shapes without breaking.
Generally, metals are malleable while non-metals and salts are not. Many non-metals and salts are brittle. Metals can be beaten to make swords, knives, springs, pots and pans and so on. [malleable vs brittle]
5. Ductility
Ductility is the ability of a substance to be drawn into wires without breaking.
Generally, metals are ductile while non-metals and salts are not. Many non-metals and salts are brittle. Metals such as copper are often drawn into wires. [ductile vs brittle]
6. Density
Density is the mass per unit volume of a substance.Generally, metals have high density while non-metals have low density.
There was an ancient Greek story about how Archimedes used the density of gold to determine if the goldsmith had committed a fraud in the manufacture of crowns by replacing some gold with silver. Read more about it at https://www.math.nyu.edu/~crorres/Archimedes/Crown/CrownIntro.html.
7. Melting point and boiling point
Melting point is the temperature at which a substance changes from solid state to liquid state at a fixed temperature.
Boiling point is the temperature at which a substance changes from liquid state to gaseous state at a fixed temperature.Generally, metals have high melting and boiling points while non-metals have low melting and boiling points.
Pure substances such as elements and compounds have fixed melting points and boiling points at a particular temperature and pressure. Impure substances such as mixtures do not have fixed melting and boiling points and also melt and boil over a range of temperatures.
Note that changes in state are physical changes, not chemical changes. Melting, boiling, evaporation, condensation, freezing, sublimation and deposition are physical changes.
Knowing the melting and boiling points of a substance also tell you the state of the substance at room temperature.
8. Electrical conductivity
Electrical conductivity is the extent to which how readily charged particles can pass through a substance.
The easier it is for charged particles to pass through a substance, the higher its electrical conductivity. Substances that allows charged particles to pass through easily are good conductors of electricity while those that do not allow charged particles to pass through easily are poor conductors of electricity or electrical insulators.
Generally, metals are good conductors of electricity while non-metals are poor conductors of electricity.
9. Thermal conductivity
Thermal conductivity is the extent to which how readily heat energy can pass through a substance.
The easier it is for heat energy to pass through a substance, the higher its thermal conductivity. Substances that allows heat energy to pass through easily are good conductors of heat while those that do not allow heat energy to pass through easily are poor conductors of heat or thermal insulators.
10. Solubility
Solubility is the extent to which a solute will dissolve in a fixed amount of solvent at a particular temperature.
11. Opacity
Opacity is the extent to which a substance prevents visible light from passing through it.
An opaque substance does not any light to pass through it. An example is any metal.
A translucent substance allows some light to pass through it. An example is baking paper.
A transparent substance allows all light to pass through it. An example is pure water.
A translucent substance allows some light to pass through it. An example is baking paper.
A transparent substance allows all light to pass through it. An example is pure water.
12. Sonority
Sonority is the ability of a substance to produce a ringing sound when struck with a hard object.
Generally, metals produce a ringing sound when hit. This is how piano produces a sound when the keyboard is struck.
13. Lustre
Lustre is the extent to which a substance can reflect evenly without glittering.
Generally, metals are lustrous and non-metals are non-lustrous.
14. Viscosity
Viscosity is the extent to which a fluid (liquid or gas) resists flowing.
Petroleum and syrup are viscous while water is fluid.
15. Magnetism
Magnetism is a property of substance that enables it to attracts or repels a magnet or magnetic material.
Magnetic materials include iron (Fe), steel (an alloy of iron, carbon and other metals), nickel(Ni), cobalt (Co) and neodymium (Nd). These are metals or metal alloys. However, not all metals are magnetic materials.
16. Colour
Most metals are silvery grey such as sodium, magnesium and iron. Some metals have attractive colour such as yellow for gold and pinkish brown for copper. Some non-metals are coloured, such as the black iodine solid or reddish brown liquid bromine at room temperature. Other non-metals are colourless such as the noble gases of helium, neon and argon..
Chemical properties
Chemical properties are properties which are observed and measured by allowing substances to undergo chemical reactions. Examples:
1. Flammability
Flammability is the ability of a substance to combust (burn and produce heat and sometimes light when mixed with oxygen in air).
This includes Group I reactive metals such as potassium and caesium and organic compounds such as hydrocarbons (think of oil and cooking gas) and alcohols (think of beer and wine). Potassium burns with a lilac (pink) flame while ceasium burns with a blue/violet flame. Mineral rocks resist burning and their flammability is low.
2. Oxidation
This is related to point 1 and 3. This property is about how readily a substance reacts with oxygen in the air.
Metals from Group I reacts readily with oxygen and as a result, they are stored in oil to prevent them from being exposed to oxygen in air.
3. Reaction with other chemicals
Usually, you will need to look at whether the substances reacts with water or acids/alkalis or with strong electronegative elements such as fluorine.
Some metals reacts readily and even explosively with water and acids such as the Group I metals (lithium, sodium, potassium, caesium) while others are quite unreactive such as gold and silver.
4. Thermal stability
Thermal stability is the extent to which a substance will decompose upon heating.
Some substances decompose easily to form new simpler substances upon heating, others do not. For example, table salt (sodium chloride) does not decompose into new substances even when heated to very high temperatures while sugar (glucose) decompose easily into carbon and water when heated.
Elements
An element is a pure substance that is made up of only one type of atom and cannot be broken down into simpler substances by physical or chemical processes.
In terms of particles, elements are substances made up of only one type of atoms. There is really nothing more simpler than having only one type of atom. That is the simplest. There is no way you can break down a substance that consists of only one type of atom to get another substance because the other substance will still be made up of only one type of atom.
Iodine is an element:
For example, when solid iodine, I2 (see below) is heated, it sublimes and turns into a gas. The distance between the iodine molecules increases but they do not break down to form new substances. Even if the iodine molecules are separated into 2 iodine atoms, only one type of atom exists. Monatomic iodine and diatomic iodine are still iodine elements. No new substances are formed.
Water is not an element:
When an electric current is passed through water, water molecules split into 2 new substances, hydrogen gas and oxygen gas. This shows that water is not made up of only one type of atoms. Water is a compound, not an element:
Particulate nature of elements
Some elements exist as single atoms while other exist as molecules. Elements that exist as single atoms are called monatomic elements. Diatomic molecules are made up of 2 atoms. Triatomic molecules are made up of 3 atoms. Polyatomic molecules consist of 3 or more atoms. There are also giant molecules in which as many atoms as possible can be chemically combined together. The number can vary. For example, a large diamond can have hundreds of millions of atoms while a smaller diamond have tens of millions of atoms.
Periodic Table of Elements
Elements can be found in the Periodic Table of Elements, which you will be learning in the topic of Periodic Table.
In the periodic table, each element is represented by a symbol, which is made of one uppercase letter, or two letters, the first being uppercase and the second being lowercase. Note the staircase or zigzag line is also known as Hays-McDaniel line.
Elements with single letter symbols
| Element Name | Symbol | Element Name | Symbol |
|---|---|---|---|
| Boron | B | Oxygen | O |
| Carbon | C | Phosphorus | P |
| Fluorine | F | Sulfur* | S |
| Hydrogen | H | Uranium | U |
| Iodine | I | Vanadium | V |
| Potassium | K | Tungsten | W |
| Nitrogen | N | Yttrium | Y |
Elements with two-letter symbols
| Element Name | Symbol | Element Name | Symbol |
|---|---|---|---|
| Silver | Ag | Magnesium | Mg |
| Aluminium | Al | Manganese | Mn |
| Argon | Ar | Molybdenum | Mo |
| Arsenic | As | Sodium | Na* |
| Astatine | At | Neon | Ne |
| Gold | Au* | Nickel | Ni |
| Barium | Ba | Lead | Pb |
| Beryllium | Be | Palladium | Pd |
| Bismuth | Bi | Polonium | Po |
| Bromine | Br | Platinum | Pt |
| Calcium | Ca | Radium | Ra |
| Cadmium | Cd | Rubidium | Rb |
| Chlorine | Cl | Rhodium | Rh |
| Cobalt | Co | Radon | Rn |
| Chromium | Cr | Antimony | Sb |
| Caesium | Cs | Scandium | Sc |
| Copper | Cu* | Selenium | Se |
| Iron | Fe* | Silicon | Si |
| Gallium | Ga | Tin | Sn |
| Germanium | Ge | Strontium | Sr |
| Helium | He | Thallium | Tl |
| Mercury | Hg | Titanium | Ti |
| Indium | In | Xenon | Xe |
| Krypton | Kr | Zinc | Zn |
**Some elements are named after countries and people: Am (americium) for America, Cf (californium) for the California state in America, Nh (nihonium) for Japan, Cm (curium) after Marie Curie, Einsteinium (Es) after Albert Einstein, Md (Mendelevium) for Dmitri Mendeleev, the chemist who came up with the first version of the modern Periodic Table
***Some elements are only discovered recently! Tennessine (Ts) was discovered in 2010!
Classification of Elements
Elements can be generally classified into three main groups: (i) metals, (ii) non-metals and (iii) metalloids.
(i) Metals
There are alkali metals (Group I), alkaline-earth metals (Group II), transition metals and others. Most of the elements are metals and are found on the left side of the table (left of the zigzag line or staircase line). Their names usually end with "-ium".
Note: Some non-metals such as helium and selenium have names ending with "-ium" and some metals such as copper, nickel, zinc, silver, gold and tungsten do not end with "-ium".
General properties of metals
- Most have shiny appearance (lustrous).
- Most metals are hard (except Group I metals such as sodium and potassium which are soft and can be cut with a knife).
- Malleable (can be hammered or beaten into different shapes without breaking) and ductile (can be drawn into wires without breaking)
- Sonorous (make a full deep sound sound when struck)
- Most have high melting and boiling points (except group I metals such as lithium, sodium and potassium).
- Most are solids at room temperature (except mercury which has a melting point -38°C and is a liquid).
- Good conductors of electricity (good electrical conductivity)
- Good conductors of heat (good thermal conduct)
- Most have high density (except Group I metals such as potassium, rubidium caesium).
Comparing melting point and boiling points
| Potassium Group I alkali metal |
Calcium Group II alkaline earth metal |
Iron Transition metal |
|---|---|---|
| melting point: 63.5°C boiling point: 759°C density: 0.89gcm-3 (even less than water!) |
melting point: 842°C boiling point: 1242°C density: 1.54gcm-3 |
melting point: 1538°C boiling point: 2861°C density: 7.87gcm-3 |
Comparing hardness
| Metal | Mohs scale |
|---|---|
| Potassium Group I alkali metal | 0.4 |
| Calcium Group II alkaline earth metal | 1.75 |
| Iron Transition metal | 4.0 |
| Vanadium Transition metal | 7.0 |
https://en.wikipedia.org/wiki/Mohs_scale_of_mineral_hardness)
Comparing electrical conductivity
| Metal | Electrical Conductivity |
|---|---|
| Magnesium Group II alkaline earth metal | 2.15 x 107 |
| Aluminium Group III metal | 3.5 x 107 |
| Gold Transition metal | 4.52 x 107 |
| Copper Transition metal | 5.98 x 107 |
| Silver Transition metal | 6.30 x 107 |
Copper and silver are very good conductors of electricity!
Comparing thermal conductivity
| Metal | Thermal Conductivity |
|---|---|
| Stainless steel (an alloy of iron) | 16.3 |
| Bronze (an alloy of copper and tin) | 26.0 |
| Iron Transition metal | 71.8 |
| Brass (an alloy of copper and zinc) | 111.0 |
| Aluminium Group III metal | 220.0 |
| Gold Transition metal | 318.0 |
| Copper Transition metal | 386.0 |
| Silver Transition metal | 418.0 |
Aluminium and copper are used in cookware. They are very good conductors of heat!
There are 118 elements in the periodic table, 90 are naturally occurring while the rest are synthesised in laboratories. Because of the vast number of elements, in the several tables of elements below, essential elements have been highlighted in magenta, while interesting elements that are used in our everyday modern electronic gadgets such as touchscreen, flatscreen TVs, and smartphones are highlighted in orange because we think a modern 21st century student should know about them.
Experiments to determine thermal conductivity
Method 1: Ingenhousz Apparatus Experiment
Procedure:
1. Prepare rods of different materials with the same thickness and length and secure them on the sides of the Ingenhousz apparatus.
2. Coat the entire length of each of the rod with a layer of paraffin wax with the same thickness.
3. Pour boiling water into the Ingenhousz apparatus.
4. After a fixed duration of time, observe the amount of wax that has melted on each of the rods.
Observation: Glass is the poorest conductor of heat while silver is the best conductor of heat. Silver is an even better conductor of heat then copper. Notice that aluminium, copper and silver are the three best conductors of heat and they are commonly used to produce kitchen pots and pans.
Method 2: Direct heating
Procedure:
1. Prepare rods of different materials with the same thickness and length.
2. Using the same amount of paraffin wax, fix a pin at the end of each rod. The pins should be situated at the same distance away from the end of each rod.
3. Observe the sequence the pins will fall off from each rod.
Observation: Glass is the poorest conductor of heat while silver is the best conductor of heat. Silver is an even better conductor of heat then copper. Notice that aluminium, copper and silver are the three best conductors of heat and they are also the three metals that are commonly used to product kitchen pots and pans.
Method 3: Conductivity Star Experiment
1. Using the same amount of paraffin wax, fix a pin at the end of each metal rod. The thickness of wax and the distance of the pin from the end of each rod should be approximately the same.
2. Heat the centre of the conductivity star apparatus using a Bunsen burner.
3. Observe the sequence the wax will melt and cause the pin to fall.
Observation: Steel is the poorest conductor of heat while copper is the best conductor of heat. The sequence is steel, nickel, brass, aluminium and then copper.
You will be learning more about metals in the topics of Periodic Table and Metals.
Uses of Group I Alkali Metals
| Element Name | Symbol | Properties and Uses |
|---|---|---|
| Lithium | Li | 1) Used to make rechargeable batteries that are used in mobile phones, laptops, digital cameras and electric vehicles. Also used in non-rechargeable batteries in heart pacemakers, toys and clocks. 2) Added to metals to improve their strength and make them lighter. Magnesium-lithium alloy for armour-plating, and aluminium-lithium alloy for aircrafts, bicycle frames and high-speed train. 3) Lithium oxide: used in glass and glass ceramics 4) Lithium chloride, lithium bromide: one of the most hygroscopic (absorbing moisture) , materials, used in air conditioning and industrial drying systems. 5) Lithium stearate: all-purpose and high-temperature lubricant 6) Lithium hydride: used for storing hydrogen gas as a fuel Listen to podcast here: https://www.rsc.org/periodic-table/podcast/3/Lithium |
| Sodium | Na | 1) Sodium chloride: used as table salt for seasoning food, to preserve food (as in salted vegetables), and to de-ice roads during winter 2) Sodium carbonate: used as water softener in household cleaning products such as laundry detergents Listen to podcast here: https://www.rsc.org/periodic-table/podcast/11/sodium |
| Potassium | K | 1) Potassium nitrate: used in making fertilisers 2) Potassium carbonate: used in making glass 3) Potassium hydroxide: used in making soaps and detergents 4) Potassium chloride: used in pharmaceuticals and saline drips Listen to podcast here: https://www.rsc.org/periodic-table/podcast/19/potassium |
| Rubidium | Rb | 1) Used in photocells 2) Very reactive in oxygen in air: used to remove oxygen from air in vacuum tubes 3) Rubidium nitrate: produce purple fireworks Listen to podcast here: https://www.rsc.org/periodic-table/podcast/37/rubidium |
| Caesium | Cs | 1) Caesium compounds: drilling liquids 2) Caesium (atomic) clock: important in modern internet and mobile phone network, and Global Positioning System (GPS) Listen to podcast here: https://www.rsc.org/periodic-table/podcast/55/caesium |
| Francium | Fr | - |
Uses of Group II Alkaline Earth Metals
| Element Name | Symbol | Properties and Uses |
|---|---|---|
| Beryllium | Be | 1) Added to alloys with copper or nickel: used to make gyroscopes, springs, electrical contacts, spot-welding electrodes and non-sparking tools. Beryllium helps to increase electrical and thermal conductivities. 2) Beryllium alloys: used as structural materials in high-speed aircrafts, missiles, spacecraft and communication satellites. 3) Allows X-rays to pass through and is applied in X-ray lithography. 4) Used a reflector/moderator of neutrons in nuclear reactors 5) Beryllium oxide: very high melting point and is used in nuclear and ceramic applications Listen to podcast here: https://www.rsc.org/periodic-table/podcast/4/beryllium |
| Magnesium | Mg | 1) Magnesium as an additive to alloys: mix with other metals such as aluminium to form strong and light alloys for aircraft bodies. 2) Magnesium is also used as a sacrificial metal: prevent rusting of iron and steel, in pipes and hulls of ships 3) Magnesium hydroxide: mixed with water to form the milk of Magnesia, which is used as an antacid for treating gastric pain. 4) Magnesium hydroxide and magnesium carbonate: toothpaste 5) Magnesium oxide: a very good refractory material with very high melting point, used to lay the inner surfaces of blast furnaces 6) Magnesium sulfate: also called Epsom salt, used to treat constipation 7) An important component of chlorophyll: a pigment necessary for photosynthesis to take place in green plants Listen to podcast here: https://www.rsc.org/periodic-table/podcast/12/magnesium |
| Calcium | Ca | 1) Calcium carbonate (limestone): used directly as a building material and indirectly as cement. 2) Calcium hydroxide (slaked lime): when limestone is heated in kilns, carbon dioxide is given off, leaving behind calcium oxide (lime). Calcium oxide reacts with water to form calcium hydroxide which is used to reduce soil acidity and to produce cement. When mixed with sand, slaked lime absorb carbon dioxide from the air to form lime plaster. 3) Calcium oxide (lime): remove acidic impurities (silicon dioxide) from molten iron in the production of steel, and use in making cement 4) Calcium sulfate (gypsum): used by builders as plaster and in medical as "plaster of Paris" for setting bones. It is also used to coagulate soy milk to make soybean curd. 5) Helps in blood clotting around wounds Listen to podcast here: https://www.rsc.org/periodic-table/podcast/20/calcium |
| Strontium | Sr | 1) Fireworks, glows red 2) Strontium aluminate: glow-in-the-dark paints and plastics. Absorbs light during the day and releases it slowing at night 3) Strontium-90: a radioactive isotope, a waste product form nuclear reaction. It is absorbed by bone tissue instead of calcium, causing cancer. It is a good emitter of high-energy beta particles. As such, it is used to generate electricity for space vehicles, remote weather stations and navigation buoys. The radioactivity can also be used to gauge thickness and removing static charges from machinery that handles paper and plastic. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/38/strontium |
| Barium | Ba | 1) Barium nitrate: green fireworks 2) All barium compounds are toxic: However, barium sulfate is insoluble and can be swallowed to treat digestive disorders. Barium is a heavy element that scatters X-rays, so it can be used to trace how the compound moves through the stomach and intestines. 3) Barite (barium sulfate): accumulates in marine sediments and reveals ocean history as a result. This is due to barite being a heavy compound and insoluble in water. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/56/barium |
| Radium | Ra | Radioactive metal: treat cancer (discovered by Marie Curie) Listen to podcast here: https://www.rsc.org/periodic-table/podcast/88/radium |
Uses of Group III Metals
| Element Name | Symbol | Properties and Uses |
|---|---|---|
| Aluminium | Al | 1) Good electrical conductivity: used as wires and cheaper than copper 2) Low density, non-toxic, good thermal conductivity, highly malleable, chemically unreactive due to the protective coating of aluminium oxide: aluminium foil, kitchen utensils, aluminium cans, window frames 3) Forms alloys with copper, manganese, magnesium and silicon that are lightweight, strong and malleable which are suitable for making aircraft bodies Listen to podcast here: https://www.rsc.org/periodic-table/podcast/13/aluminium |
| Gallium | Ga | 1) Gallium-arsenide: an important semiconductor*; used in LEDs (light-emitting diodes) and solar panels because of their ability to convert electricity into light. 2) Gallium-nitride: also a semiconductor: used in Blu-ray DVD technology, mobile phones, blue and green LEDs, and pressure sensors for touch switches Listen to podcast here: https://www.rsc.org/periodic-table/podcast/31/gallium |
| Indium | In | 1) Indium Tin Oxide (ITO): used in touchscreens, flatscreen LCD (liquid crystal display) TVs and solar panels because it conducts electricity, can stick to glass and is transparent. 2) Indium nitride (InN), indium phosphide (InP) and indium antimonide (InSb): these are semiconductors used in transistors and microchips 3) Conform to irregular surfaces very well and stick to other metals very well: used on cryogenic** pumps, high vacuum system and solder. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/49/indium |
| Thallium | Tl | 1) Thallium oxide: used to make glass with high refractive index and low melting glass which is suitable to use in electronics as the glass does not shatter like normal glass 2) Thallium sulfide: used in electronics industry, because its conductivity changes when exposed to infrared. 3) Thallium bromide-iodide crystals: used in infrared detectors 4) Used in high temperature semiconductor industry Listen to podcast here: https://www.rsc.org/periodic-table/podcast/81/thallium |
*semiconductors: materials with electrical conductivity between that of metals and non-metals. Their resistance falls as temperature rises.
**cryogenic: the production and behaviour of materials at very low temperatures
Uses of Group IV Metals
| Element Name | Symbol | Properties and Uses |
|---|---|---|
| Tin | Sn | 1) No reactivity with water and dilute acids: used to make tin-coated steel for making "tin" cans as it prevents the steel from rusting 2) Tin(IV) oxide: used in ceramics and gas sensors 3) Added to copper to make bronze, which is harder than copper, easier to mould and sharpen 4) Also used to make other alloys: pewter, solder 5) Most tonally resonant metal: mix with lead in a 50%-50% composition to make bell metals and organ pipes Listen to podcast here: https://www.rsc.org/periodic-table/podcast/50/tin |
| Lead | Pb | 1) Corrosion-resistant: used to store corrosive liquids 2) Used in car batteries (lead-acid batteries), pigments (added to paint for colour, to accelerate drying and to resist corrosion), radiation protection against gamma rays, and in some solders Listen to podcast here: https://www.rsc.org/periodic-table/podcast/82/Lead |
Uses of Transition Metals
| Element Name | Symbol | Properties and Uses |
|---|---|---|
| Scandium | Sc | - |
| Titanium | Ti | 1) As strong as steel but much less dense: it is added to other metals such as aluminium, molybdenum and iron to form alloys that are strong, lightweight (low density) and able to withstand extreme temperatures. These alloys are used in aircraft, spacecraft, missiles and also in golf clubs, crutches, and bicycles. 2) Excellent resistance to corrosion: used in desalination plants as pipes, protect the hull of ships, submarines and other structures exposed to seawater. 3) Non-toxic and corrosion-resistant: used as hip replacement and tooth implants in human bodies 4) White titaniun(IV) oxide: used as pigments in paints and artists' paint because of its bright white colour and excellent covering power. 5) Titanium(IV) oxide: able to absorb UV (ultraviolet) light, used in sunscreen as nanoparticles of titanium(IV) oxide are excellent blockers of sunlight and are transparent when applied to skin. After absorbing UV light, it releases electrons, making useful in photocatalyst. 6) White and non-toxic: toothpaste Listen to podcast here: https://www.rsc.org/periodic-table/podcast/22/titanium |
| Vanadium | V | 1) Used as steel additives to produce alloys that are very tough: used to make armour plates and heavy duty tools 2) Used in nuclear reactors because vanadium allows have low neutron-absorbing property 3) Black vanadium(V) oxide or vanadium pentoxide: used as a catalyst in producing concentrated sulfuric acid 4) Due to its many oxidation states, it has significant effects on cellular growth, redox, signal processes and enzyme functions. It also mimics the action of the hormone insulin. Vanadium is important in the vanadium nitrogenase, an enzyme that reduces dinitrogen to ammonia in the root nodules of many plants. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/23/vanadium |
| Chromium | Cr | 1) Corrosion-resistance: added to iron to make stainless steel (does not rust). Chromium reacts with oxygen to form 2) Chromium compounds are used as industrial catalysts and colour pigments: dark red chromium(VI) oxide, orange red lead(II) chromate PbCrO4, bright yellow sodium chromate(VI), Na2CrO4, orange potassium dichromate(VI) K2Cr2O7, bright green chromium(III) oxide, light blue chromium(II) chloride CrCl2, and violet anhydrous chromium(III) chloride. Rubies are red due to chromium and glass treated with chromium has an emerald green colour. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/24/chromium |
| Manganese | Mn | 1) Added to steel to increase strength and and resistance to wear and tear. Suitable for railway tracks. 2) Added to aluminium to improve resistance to corrosion for drink cans. 3) Manganese(IV) oxide: used as a catalyst and to decolourise glass that has been tainted green by iron impurities. This is also used as a catalyst to break down hydrogen peroxide into water and oxygen. 4) Manganese sulfate: fungicide 5) Like vanadium, because it has many oxidation states, and is significant in many biological enzymatic functions: fungi uses an enzyme, manganese peroxidase oxidise manganese(+2) to manganese(+3), which is highly reactive and can break down the tough lignin tissues in wood, making them available as food for the fungi Manganese is also key to the photosynthesis process, enabling water molecules to be split into oxygen atoms. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/25/manganese |
| Iron | Fe | 1) Used to manufacture steel, which is an alloy of mainly iron mixed with carbon and small amounts of other metals such as chromium and manganese to improve resistance to corrosion and strength 1.1) Cast iron: 3-5% carbon, brittle and not as strong as steel: used for pipes, valves and pumps 1.2) High carbon steel: iron + 2-3% carbon 1.3) Mild steel: iron + 0.1% carbon 1.4) Stainless steel: iron + carbon + chromium, very resistance to corrosion. Other metals such as nickel, copper, molybdenum and titanium are added to improve strength. Used to make surgical instruments, cutlery, jewellery and kitchen equipment. 1.5) Alloy steels: iron + carbon + other metals such as nickel, chromium, vanadium, tungsten and manganese to increase strength. Used to make bridges, bicycle chains, cutting tools and rifle barrels. 2) Iron and its alloys can be made into magnets. 3) An important component of haemoglobin, the protein that absorbs oxygen in red blood cells 4) Causes many neurodegenerative diseases when iron accumulates in the neurons found in brains Listen to podcast here: https://www.rsc.org/periodic-table/podcast/26/iron |
| Cobalt | Co | 1) A magnetic material:can be made into magnets. Alloyed with aluminium and nickel to make powerful magnets which can retain magnetism even at high temperature. 2) Alloys of cobalt can withstand high temperatures and have great strength: used to make jet turbine and gas turbine generators 3) Shiny and silvery blue: used in electroplating because of their attractive appearance, hardness and resistance to corrosion. 4) Cobalt salts are used as blue pigments in paints, glass and porcelain. 5) Cobalt-60 is radioactive and emits gamma rays. It is used to treat cancer in radiotherapy treatment and to irradiate food for preservation. 6) Cobalt(II) chloride is used as a moisture indicator: in the anhydrous form, it is blue; in the hydrated form, it is pink. It is found in science laboratories as cobalt(II) chloride paper. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/27/cobalt |
| Nickel | Ni | 1) A magnetic material: can be used to make into magnets 2) Used in batteries: nickel-cadmium batteries, and nickel-metal hydride batteries 3) Highly resistance to corrosion even at high temperature: used to electroplating to protect other metals; added to steel (iron + carbon) to make stainless steel (do not rust) 4) Nichrome: an alloy of nickel and chromium, and small amounts of silicon, manganese and iron. Use as a heating element in kettles, toasters and electric ovens because it has very high melting point, and able to resist corrosion even when red-hot. 5) Copper-nickel alloy: able to resist corrosion, used in desalination plant where saltwater is converted into freshwater. Also used to make coins. 6) Finely divided nickel is used as a catalyst in hydrogenation process where vegetable oils is converted into margarine 7) Added to glass to make it green 8) Aluminium-nickel superalloy which is light and becomes stronger and harder the more it is heated, used in aircraft and rocket turbines. 9) Memory metal alloy: able to return to its original shape even after bending and twisting Listen to podcast here: https://www.rsc.org/periodic-table/podcast/28/nickel |
| Copper | Cu | 1) Ductile, good thermal conductivity and electrical conductivity: can be drawn into wires to make wiring and motors; used to make heat exchange pipes 2) Attractive shiny pinkish-brown colour, resistant to corrosion: made into coins 3) Copper and tin are mixed to make bronze, which is used to make sculptures, tools and medals 4) Copper(II) sulfate: used as an algaecide, useful for dealing with algae blooms, as well as pesticide and fungicide 5) Copper compounds, such as Fehling's solution, are use to test for sugar. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/29/copper |
| Zinc | Zn | 1) Like magnesium, zinc is used as a sacrificial metal to protect iron from rusting. Galvanised steel (steel coated with a layer of zinc) is used roofing, car bodies, street lamp posts and suspension bridges 2) Added to copper to produce brass, an alloy that is tough and has a shiny yellow colour for making electric plugs and brass musical instruments 3) Zinc oxide: used to manufacture a wide variety of products such as paints, rubber, cosmetics, pharmaceuticals, plastics, inks, soaps, batteries, textiles and electrical equipment. Like titanium(IV) oxide, zinc oxide is an effective UV ray blocker and is used in sunscreen lotion, anti-dandruff shampoo and calamine lotion 4) Zinc sulfide: used in luminous paints, fluorescent lamps and X-ray screen 5) Used in dry cell batteries, acting as the anode (negative end) of the batteries Listen to podcast here: https://www.rsc.org/periodic-table/podcast/30/zinc |
*oxidation state: also called oxidation number, is the degree of oxidation (electron loss) of an element.
Uses of Rare Earth Metals
These are highly valuable and highly demanded metals in the modern world today! If you use high-tech electronic devices such as laser pointers, high-speed fibre-optic internet, smartphones, computers, and flatscreen TVs, you are bound to encounter them!
Rare earth metals consists of 17 elements, scandium, yttrium and 15 lanthanoids or lanthanides.
| Element Name | Symbol | Properties and Uses |
|---|---|---|
| Scandium | Sc | Scandium iodide is added to mercury vapour lamps to produce a highly efficient light source resembling sunlight. This is used in floodlights and film projections. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/21/scandium |
| Yttrium | Y | 1) Added to glass to make camera lenses that are heat and shock resistant 2) Increase the strength of aluminium and magnesium alloys 3) Acts as a catalyst in ethene polymerisation (making of plastics) 4) Making microwave filters for radar (radio detection and ranging) 5) Used in lasers that cut through metals 6) Used in white LEDs 7) Yttrium aluminium garnet, YAG is an important synthetic mineral, used to make artificial diamonds. Also, by adding small amount of other lanthanides, very useful materials can be derived. Add some neodymium and you get solid state laser material. Add some ebrium and you get infrared laser. 8) Yttria-stabilised zirconia, YSZ: a substance made by adding yttrium oxide to zirconium oxide, it is used widely in fuel cells because it produces conducting oxide ions*. It is also used to make lambda sensors in cars which can monitor the amount of oxygen in car exhaust and sends feedback to the system to ensure the optimum air-fuel mixture in car engines. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/39/yttrium |
| Lanthanum | La | 1) Used in electric cars: lanthanum-nickel alloy is used to store hydrogen in hydrogen-powered vehicles. Used in nickel metal hydride batteries in hybrid cars. 2) Used in lighting application as they are bright and their emission spectrum is similar to sunlight 3) Lanthanum(III) oxide: make special optical glass, improves the optical properties and alkaline resistance of glass 4) Lanthanum salts: used as catalysts in petroleum refining Listen to podcast here: https://www.rsc.org/periodic-table/podcast/57/lanthanum |
| Cerium | Ce | 1) Used as a catalyst: used in self-cleaning oven to prevent build-up of food residues. Also used in catalytic converters as cerium dioxide to help combust unburnt hydrocarbons. As a nanopowder, it can be mixed with diesel fuels to reduce the amount of soot formed. 2) Used in flat-screen TVs, low energy light bulbs and floodlights Listen to podcast here: https://www.rsc.org/periodic-table/podcast/58/cerium |
| Praseodymium | Pr | 1) See neodymium. Used to make didymium glass 2) Used in alloys to make powerful permanent magnets: used in electric motors and electronic devices 3) Forms high-strength alloys with magnesium to make aircraft engines 4) Used in lighting application as they are bright and their emission spectrum is similar to sunlight Listen to podcast here: https://www.rsc.org/periodic-table/podcast/59/praseodymium |
| Neodymium | Nd | 1) Neodymium iron borate, an alloy of neodymium, iron and boron are used to make permanent magners 1000 times more powerful than normal magnets: enables miniaturisation of many electronic devices such as mobile phones, microphones, loudspeakers, electronic musical instruments, car windscreen wipers and wind turbines. 2) Used in making tanning glass as it allows UV light to pass through and absorbs infrared radiation 3) Adding neodymium to YAG (yttrium-aluminium garnet, a synthetic diamond), produces industrial laser cutting tools with bright infrared liens 4) Neodymium oxide: catalyst in polymerisation reactions 5) Neodymium and praseodymium are used to make didymium glass, which is used to make special googles for welding because it filters out yellow light and infrared radiation. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/60/neodymium |
| Promethium | Pm | 1) A radioactive metal with nuclear applications. Used as a source of X-ray when its beta particles (electrons) hit heavy nuclei. The x-rays are used to measure the thickness of materials. 2) Upon decay, its beta radiation cause phosphor (not the element phosphorus) to give off light which can be absorbed by a solar cell. 3) Promethium-147: its decay produces beta (electron) particles which are used nuclear batteries as they are long-lasting as well Listen to podcast here: https://www.rsc.org/periodic-table/podcast/61/promethium |
| Samarium | Sm | 1) Samarium-cobalt magnets are more powerful than iron magnets. Hence, they are used in microwave ovens and are used to miniaturise electronic devices such as headphones and personal stereo. However, this type of magnets is gradually replaced by neodymium magnets. 2) Dope calcium chloride in optical laser. 3) Used in infrared absorbing glass 4) Used in lighting application to produce bright white light that resembles sunlight. 5) Can absorb neutrons, used in nuclear reactors to control chain reactions, often mix with europium and gadolinium to form the samarium-europium-gadolinium (SEG) concentrate. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/62/samarium |
| Europium | Eu | 1) Used in printing Euro banknotes: it glows red under UV light and forgeries can be detected by the lack of red glow. 2) Used in low energy light bulbs to produce a more natural glow by balancing cool blue light with warm red light. 3) Can absorb neutrons, used in nuclear reactors to control chain reactions. See samarium's samarium-europium-gadolinium (SEG) concentrate. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/63/europium |
| Gadolinium | Gd | 1) Added to alloys to increase resistance to high temperatures and oxidation. The alloys are used to make magnets, electronic components and data storage disks 2) Gadolinium compounds are used in magnetic resonance imaging (MRI), for diagnosing tumour 3) Can absorb neutrons, used in nuclear reactors to control chain reactions. See samarium's samarium-europium-gadolinium (SEG) concentrate. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/64/gadolinium |
| Terbium | Tb | 1) Used to dope calcium fluoride, calcium tungstate, and strontium molybdate in solid-state electronic devices. 2) Terbium salts emit green colour: used in low energy light bulbs and laser devices 3) Used to improve safety of X-ray medical devices by producing images with same quality but with shorter exposure time. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/65/terbium |
| Dysprosium | Dy | 1) An alloy additive in neodymium-alloy magnets because it resists demagnetisation at high temperatures. Useful for motors and generators. 2) Dyprosium iodide is used in lighting application to produce intense white light. 3) Dysprosium oxide-nickel ceramic composite material: can absorb neutrons, used in nuclear reactors to control chain reactions 4) Magnetostrictive: changes its shape when put under a magnetic field. This is applied in ships' sonar systems, sensors and transducers**. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/66/dysprosium |
| Holmium | Ho | Can absorb neutrons, used in nuclear reactors to control chain reactions Listen to podcast here: https://www.rsc.org/periodic-table/podcast/67/holmium |
| Erbium | Er | Erbium in glass fibres is used to amplify broadband signals in fibre-optic cables Listen to podcast here: https://www.rsc.org/periodic-table/podcast/68/erbium |
| Thulium | Tm | 1) Thulium produces an isotope that radiates X-rays. A nugget of it is used to make a lightweight portable X-ray machine. 2) Used in lasers for surgical applications. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/69/thulium |
| Ytterbrium | Yb | 1) In electronic memory devices 2) In tuneable lasers 3) As a catalyst 4) Used in biological and biomedical research in light microscopy because human cells are more transparent when exposed to infrared, revealing more depth in structure Listen to podcast here: https://www.rsc.org/periodic-table/podcast/70/ytterbium |
| Lutetium | Lu | As a catalyst for cracking hydrocarbons in oil refining industry. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/71/lutetium |
*ions: these are charged particles formed by the gaining or losing of electrons by an atom or a group of atoms.
**transducers: a device that converts non-electrical properties such as pressure or light into electrical energy
What are some of the ways that you can better remember the properties of different metals?
(ii) Non-metals
There are halogens (Group VII) and noble gases (Group 0). Non-metal elements are much fewer than metal elements and are found on the right side of the table (right of the zigzag line or staircase line).
General properties of non-metals
- Most are dull (non-lustrous).
- Most are brittle (not malleable and ductile).
- Most have low melting and boiling points (except diamonds).
- Most are gases and volatile* liquids at room temperature.
- Poor conductors of electricity (except graphite)
- Poor conductors of heat
- Most have low density.
*volatile: a term used to describe a liquid that evaporates easily at room temperature. This is usually due to the low boiling point of the liquid.
Uses of Group IV Non-Metals| Element Name | Symbol | Properties and Uses |
|---|---|---|
| Carbon | C | 1) Hydrocarbons: carbon is able to form strong bonds with other carbon atoms, forming long chains, and with hydrogen to form hydrocarbons. These are found in petroleum, which is the major source of fuel for cars, trains and airplanes and also provide the chemical feedstock to manufacture many modern materials such as plastics, paints, solvents and fertilisers. 2) Impure carbon: charcoal (from wood) for cooking food, and coke (from coal) for iron extraction 3) Carbon exists in many forms called allotropes*: 3.1) Diamonds: the hardest known substance, used as drilling tips to cut rocks. Diamond film is used to protect razor blades. Diamonds also have the highest thermal conductivity, good at dissipating that and always feel cold to touch. 3.2) Graphite: used in pencils and as carbon brushes in electric motors 3.3) Activated charcoal: purification and filtration 3.4) Carbon nanotubes, fullerences and graphene: important applications in electronic industry 3.5) Carbon fibres: strong lightweight material used in fishing rods, skis and tennis rackets 4) Carbon dioxide: a greenhouse gas that helps to keep the Earth warm. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/6/carbon |
*allotropes: different forms of an element.
Uses of Group V Non-Metals (the pnictogens)
| Element Name | Symbol | Properties and Uses |
|---|---|---|
| Nitrogen | N | 1) Used in the Haber process to produce ammonia. Ammonia is then used to make fertilisers, nitric acid, nylon, dyes and explosives. 2) Very unreactive: used to preserve food, in the electronics industry to produce transistors and diodes, and in annealing steel in the steelmaking process because it does not react with steel. 3) Liquid nitrogen: used as refrigerant, for freeze-drying foods to maintain nutrition, colour, texture and flavour, and for medical purposes such as preserving sperms, eggs and other cells. 4) Sodium azide: when triggered, this compound decomposes and inflates air bags with nitrogen. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/7/nitrogen |
| Phosphorus | P | 1) White phosphorus: poisonous and flammable when exposed to air. Used in flares and incendiary devices. 2) Red phosphorus: non-toxic and is used on the side of matchboxes for matches to strike against them 3) Phosphates: important source of fertilisers, for example, ammonium phosphate. 3) Metal phosphides (e.g. gallium phosphide, indium phosphide): super pure phosphorus is used to make LEDs (light emitting diodes) Listen to podcast here: https://www.rsc.org/periodic-table/podcast/15/phosphorus |
(Source: Royal Society of Chemistry https://www.rsc.org/periodic-table/)
Uses of Group VI Non-Metals (the chalcogens)
Uses of Group VI Non-Metals (the chalcogens)
| Element Name | Symbol | Properties and Uses |
|---|---|---|
| Oxygen | O | 1) Used in steel industry to combust coke (carbon) 2) Used to making a wide range of chemicals such as nitric acid, hydrogen peroxide, polyesters, and antifreeze. 3) Used in oxy-acetylene welding and cutting of metals 4) Used in sewage treatment Listen to podcast here: https://www.rsc.org/periodic-table/podcast/8/oxygen |
| Sulfur | S | 1) Vulcanisation of rubber 2) Fungicide, herbicide, pesticide 3) Gunpowder 4) Production of sulfuric acid, which is used to make phosphoric(V) acid which in turn is used to make fertilisers 5) Sulfites: used to bleach paper and preserve food (for example, in packaged ham) 6) Sulfates: used in detergents and surfactants 7) Calcium sulfate (gypsum): used by builders as plaster and in medical as "plaster of Paris" for setting bones. It is also used to coagulate soy milk to make soybean curd. (see Calcium) Listen to podcast here: https://www.rsc.org/periodic-table/podcast/16/sulfur |
| Selenium | Se | 1) Additive to glass: it can decolourise glass, or give a red tint. It 2) Used as colour pigments to paints, ceramics and plastics 3) Has photovoltaic (converts light into electricity) and photoconductive (electrical resistances decreases with increased illumination) properties: used in solar cells, photocells, and photocopiers 4) Can convert AC (alternating current) to DC (direct current): used as rectifiers 5) Toxic to scalp fungus: used in some anti-dandruff shampoo Listen to podcast here: https://www.rsc.org/periodic-table/podcast/34/selenium |
(Source: Royal Society of Chemistry https://www.rsc.org/periodic-table/)
Uses of Group VII Non-Metals (the halogens)
Uses of Group VII Non-Metals (the halogens)
| Element Name | Symbol | Properties and Uses |
|---|---|---|
| Fluorine | F | 1) Uranium hexafluoride: used in nuclear power industry to separate uranium isotopes 2) Sulfur hexafluoride: insulating gas for high-power electrical transformers 3) Used to make Teflon (or PTFE, poly(tetrafluorethene): it is heat-resistant and non-sticky, used in frying pans and cable insulation. It is also the basis of Gore-Tex for waterproof shoes and clothing. 4) Hydrofluoric acid (HF): etching/frosting glass 5) CFCs (chloroflurocarbons): these fluro-compounds used to be found in aerosol propellants and refrigerants, but they are now banned as they destroy the ozone layer 6) Fluorides are used in toothpaste to prevent tooth decay. 7) Fluoroelastomers: a type of fluorinated rubber that are used in sealing applications and help aircraft to remain leakage-free even under extreme temperatures of heat and cold. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/9/fluorine |
| Chlorine | Cl | 1) A disinfectant: kills bacteria and is added to drinking water and swimming pool and treat sewage 2) Used to make PVC (polyvinylchloride): a plastic used in window frames, car interior, electrical wiring insulation, and water pipes 3) Pharmaceutical industry: used in various process during the manufacturing of drugs 4) Used to make chloroform (trichloromethane), an anaesthetic, and tetrachloromethane (carbon tetrachloride), a dry-cleaning solvent: both are toxic to livers and are very controlled in usage 5) Very toxic, used as a chemical weapon during World War One Listen to podcast here: https://www.rsc.org/periodic-table/podcast/17/chlorine |
| Bromine | Br | 1) Used as flame retardants: added to furniture foam and plastic casing for electronics products to make them less flammable 2) Used in certain fire extinguishers 3) Silver bromide: used in film photography 4) Used as a distinguishing test between a saturated and an unsaturated hydrocarbons Listen to podcast here: https://www.rsc.org/periodic-table/podcast/35/bromine |
| Iodine | I | 1) Polarising filters for LCD displays 2) Added to table salt (sodium chloride) to prevent deficiency in iodine which leads to thyroid gland swelling (goitre) 3) Iodine-131: a radioisotope used to treat cancerous thyroid gland Listen to podcast here: https://www.rsc.org/periodic-table/podcast/53/iodine |
| Astatine | At | - |
Uses of Group 0 Non-Metals (the nobles gases)
| Element Name | Symbol | Properties and Uses |
|---|---|---|
| Helium | He | 1) Used for filling balloons, weather balloons and airships. This replaces the flammable hydrogen gas which had resulted in disastrous explosions in the past. 2) Very low negative melting point: used as cooling medium in Large Hadron Collider (LHC) and superconducting magnets in MRI scanner and NMR spectrometer. Used to cool satellite instruments and liquid oxygen and hydrogen in rocket fuel tanks. 3) Very unreactive: provide inert protective atmosphere for making fibre-optics and semiconductors and arc welding 4) Very light gas and can diffuse quickly: detect leaks, for example, in car air-conditioning system and inflate car air-bags 5) Mixture of helium (80%) and oxygen (20%) for diving tanks for deep-sea divers 6) Helium-neon gas lasers for scanning barcodes in supermarkets 7) Helium-ion microscope provides better resolution than scanning electron microscope Listen to podcast here: https://www.rsc.org/periodic-table/podcast/2/helium |
| Neon | Ne | 1) Used to make neon signs for advertising. Neon in vacuum tubes glows red. 2) Used to make high-voltage indicators, lightning arresters, diving equipment and lasers. 3) Important cryogenic refrigerant, 40 times refrigerating capacity than that of liquid helium and 3 times that of liquid hydrogen. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/10/neon |
| Argon | Ar | 1) Used where an inert atmosphere is needed: in welding to protect weld area to prevent the metal from reacting with oxygen in air, to prevent tungsten filament in incandescent light bulbs from oxidising/corroding, helps in the production of titanium and other reactive metals to prevent them from being oxidised 2) Used in fluorescent tubes 3) Low-energy light bulbs often contains argon and mercury and this produces UV light when an electric discharge passes through the gas. Coating on the insides of the bulb is activated by the UV(ultraviolet) light and glows brightly. 4) Double-glazed windows used argon to fill the space between the panes. Argon is a poorer conductor of heat than air. 5) Car tyres filled with argon to protect them. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/18/argon |
| Krypton | Kr | 1) Inert: used as filling gas in some energy-saving light bulbs 2) However, reactive enough to form compounds with very electronegative elements such as fluorine: krypton fluoride is used in some lasers. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/36/krypton |
| Xenon | Xe | 1) Used in specialised light sources: produces blue glow when an electric discharge passes through the gas. Xenon lamps are used in high-speed electronic flash bulbs used by photographers, sunbed lamps and bactericidal lamps in food preparation and processing. 2) Used in ruby lasers 3) Xenon ion propulsion system used by satellites to keep them in orbit 4) Xenon, although inert, is reactive enough to form compounds with very electronegative elements such as flourine: xenon difluoride, used to etch silicon microprocessors; 5-fluorouracil, used to treat certain cancers Listen to podcast here: https://www.rsc.org/periodic-table/podcast/54/xenon |
| Radon | Rn | Radioactive, decays into polonium and alpha particles. Used to treat cancer. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/86/radon |
Metals vs Non-Metals
Comparing the properties of metals and non-metals
| Metals | Non-metals |
|---|---|
|
|
(iii) Metalloids
Metalloids are elements with properties between that of metals and non-metals.
General properties of metalloids
- All are solids at room temperature.
- They are generally shiny silvery grey, similar to metals
- They are less electrically conductive than metals. They are semi-conductors, and conducts electricity well under certain right conditions. For example, at certain temperatures or after being doped with certain elements.
- They are less brittle than non-metals.
| Element Name | Symbol | Properties and Uses |
|---|---|---|
| Boron | B | 1) Used as rocket fuel igniter and pyrotechnic flares giving a distinctive green colour 2) Boric oxide: used in manufacturing borosilicate glass (Pyrex). It makes the glass tough and heat resistant. Fibreglass textiles and insulation are made from borosiliate glass. 3) Boric acid and borax (sodium borate): these are found in eye drops, mild antiseptics, washing powders and tile glazes 4) Borax: used in bleaches and food preservatives 5) Sodium octaborate: flame retardant 6) Boron-10: good at absorbing neutrons. Used in neutron-detecting instruments and for regulating nuclear fission chain reaction Listen to podcast here: https://www.rsc.org/periodic-table/podcast/5/boron |
| Silicon | Si | 1) Used extensively in semiconductor industry to make solid-state electronics components. This requires hyperpure silicon and workers work in clean-room environment. Selectively doped with small amount of boron (Group III), gallium (Group III), arsenic (Group V) and phosphorus (Group V) to control its electrical properties. 2) Strong and heat-resistant: granite and most rocks are complex silicates and are used in construction. Sand (silicon dioxide or silica) and clay (aluminium silicate) are used to make concrete and cement. Sand is used to make glass. Silicon, as silicate, is used in pottery, ceramic and enamel. 3) Silicone: these are silicon-oxygen polymers with methyl groups (-CH3) attached. Silicone oil is a lubricant and is used in cosmetics and hair care products. Silicone rubber is used as a sealant in bathrooms, windows, pipes and roofs. As it is non-toxic and flexible, silicone rubber is used in to make moulds such as ice cube trays or muffin baking trays and used as implants in human bodies. 4) Silicon carbides are hard and are important abrasives. 5) Aluminium-silicon and iron-silicon (ferro-silicon) alloys (called zeolites or molecular sieves or molecular honeycombs) allow magnetic flux to pass through and are used to make dynamos and transformers. The silicon reduces the amount of induced current produced. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/14/silicon |
| Germanium | Ge | 1) Germanium oxide: has high index refraction and dispersion, and is used in wide-angle camera lens, objective lens for light microscopes and fibre-optics 2) Used as an alloying agent: added to silver to prevent it from tarnishing Listen to podcast here: https://www.rsc.org/periodic-table/podcast/32/germanium |
| Arsenic | As | 1) Well-known poison 2) Organoarsenic compounds are added to poultry feed to prevent disease and improve weight gain. 3) A doping agent for semiconductor material (gallium-arsenide) in solid-state devices to improve electrical properties 4) Arsenic compounds are used to make special glass and preserve wood. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/33/arsenic |
| Antimony | Sb | 1) Used in semiconductor devices, such as infrared detectors and diodes 2) Used as an alloying agent to improve strength and hardness. Lead-antimony alloy is used in batteries. 3) Antimony compounds are used as flame retardants in paints, glass and pottery. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/51/antimony |
| Tellurium | Te | 1) A catalyst in oil refining process 2) Can be doped with silver, gold, copper and tin in semiconductor applications 3) Cadmium telluride: capture solar energy in the most efficient manner Listen to podcast here: https://www.rsc.org/periodic-table/podcast/52/tellurium |
| Polonium | Po | 1) A radioactive metal, emitting alpha particles: used for nuclear research 2) Able to emit large quantity of heat for a very small mass due to its radiation activity. This makes it useful as an energy source for space equipment. Listen to podcast here: https://www.rsc.org/periodic-table/podcast/84/polonium |
Compounds
A compound is a pure substance made up of two or more different elements chemically combined together and can be broken down into simpler substances through chemical processes.
As such, compounds consist of at least 2 atoms. There are no compounds that exist as single atoms, unlike elements.
The atoms must also be chemically combined in fixed ratios. You can observe this in the molecular formula. For example, water has the molecular formula, H2O. The ratio of hydrogen atoms to oxygen atoms is 2:1. Just by adding another oxygen atom to water will change the ratio and turn it into a completely different compound called hydrogen peroxide, H2O2. The ratio of hydrogen atoms to oxygen atoms is 2:2, or 1:1 after simplifying.
Percentage composition by mass
Instead of using ratio, a standard way to express the composition of a molecule is by calculating the percentage composition by mass. You will learn more in the topic of Chemical Calculations. For now, see some brief examples below.
Molecules which have the same ratio of elements will have the same percentage composition by mass. For example, there is a compound called ethene, with a molecular formula of C2H4, and propene, with a molecular formula of C3H6. Both have a ratio of carbon atoms to hydrogen atoms of 1:2. For both of them, the percentage composition by mass of C is 85.71% and of H is 14.29%.
You have to refer to the Periodic Table of Elements for the relative atom mass (Ar) of the respective element to find the relative molecular mass (Mr) of the molecule. You will learn more about how to use the periodic table in the topic of Periodic Table of Elements.
Ar: C=12, H=1
| Ethene, C2H4 | Propene, C3H6 |
|---|---|
| Mr = 2 x 12 + 4 x 1 = 28 Total Ar of C = 2 x 12 = 24 Total Ar of H = 4 x 1 = 4 % composition by mass of C = 24 / 28 x 100% = 85.71% % composition by mass of H = 4 / 28 x 100% = 14.29% This means that if there are 100g of C2H4, there are 85.71g of C and 14.29g of H. |
Mr = 3 x 12 + 6 x 1 = 42 Total Ar of C = 3 x 12 = 36 Total Ar of H = 6 x 1 = 6 % composition by mass of C = 36 / 42 x 100% = 85.71 % composition by mass of H = 6 / 36 x 100% = 14.29% This means that if there are 100g of C3H6, there are 85.71g of C and 14.29g of H. |
Ar:H=1, O=16
| Water, H2O | Hydrogen Peroxide, H2O2 |
|---|---|
| Mr = 2 x 1+ 16 = 18 Total Ar of H = 2 x 1 = 2 Total Ar of O = 16 % composition by mass of H = 2 / 18 x 100% = 11.11% % composition by mass of O = 16 / 18 x 100% = 88.89% This means that if there are 100g of H2O, there are 11.11g of H and 88.89g of O. |
Mr = 2 x 1 + 2 x 16 = 34 Total Ar of H = 2 x 1 = 2 Total Ar of O = 2 x 16 = 32 % composition by mass of H = 2 / 34 x 100% = 5.88% % composition by mass of O = 32 / 34 x 100% = 94.12% This means that if there are 100g of H2O2, there are 5.88g of H and 94.12g of O. |
Synthesis of compounds
Synthesis is the process combining elements or simpler compounds to form a more complex compound. Elements are combined in a process called chemical reaction, where atoms are rearranged in a new structure to produce new compounds. Below are some examples. These examples also attempts to illustrate how to look for clues (colour changes, state changes) to determine if a new compound has been produced.
1. Synthesis of ammonia
This involves the reaction of two neutral gases to form another gas which is alkaline. Note that this is a reversible reaction. A reversible reaction in which the product that is formed also breaks down to form back the reactants.
nitrogen + hydrogen <-----> ammonia
N2(g) + 3H2(g) <-----> 2NH3(g)
Both nitrogen and hydrogen are colourless, odourless, neutral gases. Nitrogen gas is very stable and do not readily take part in reactions while hydrogen gas is very flammable with oxygen in air. They react to form ammonia, which is a colourless, pungent, alkaline gas which turns moist red litmus blue. Note that properties of the new compound formed are different from the elements it is made up of.
2. Synthesis of magnesium oxide
This involves the combustion (burning) of solid magnesium metal with oxygen gas to form a solid black compound.
magnesium + oxygen -----> magnesium oxide
2Mg(s) + O2(g) -----> 2MgO(s)
Magnesium is a shiny silvery grey solid metal at room temperature while oxygen gas is colourless, odourless and neutral gas. During combustion, magnesium burns with an intense white flame, forming a new white solid, magnesium oxide. Note that properties of the new compound formed are different from the elements it is made up of.
3. Synthesis of copper(II) chloride
The involves the reaction of solid pinkish-brown copper metal with yellowish-green chlorine gas to form a solid bluish-green salt.
copper + chloride -----> copper(II) chloride
Cu(s) + Cl2(g) -----> CuCl2(s)
Copper is a pinkish-brown solid at room temperature while chlorine is a yellowish-green gas. The product is a solid bluish-green salt, copper(II) chloride. Note that properties of the new compound formed are different from the elements it is made up of.
4.Synthesis of iron(III) chloride
This involves the reaction of silvery grey solid iron metal with yellowish-green chlorine gas to form a solid yellow salt, iron(III) chloride.
iron + chlorine -----> iron(III) chloride*
2Fe(s) + 3Cl2(g) -----> 2FeCl3(s)
Iron(III) chloride is also known as ferric chloride.
Iron is a shiny silvery grey solid metal at room temperature while chlorine is a yellowish-green gas. The reaction is vigorous, as chlorine gas is quite reactive, giving off a bright flame. The new compound form is a yellow solid iron(III) chloride. Note that properties of the new compound formed are different from the elements it is made up of.
5. Synthesis of iron(II) sulfide
This involves the reaction of silvery grey solid iron metal and solid sulfur powder to form a solid black compound.
iron + sulfur -----> iron(II) sulfide
Fe(s) + S*(s) -----> FeS(s)
Although sulfur generally exists as a molecule consisting of 8 sulfur atoms, in chemical equations, it is usually written as S only.
Iron is a shiny silvery grey solid metal while sulfur is a yellow powdery solid at room temperature. After the reaction, a new dull black compound, iron(II) sulfide, is formed. Note that properties of the new compound formed are different from the elements it is made up of.
6. Synthesis of water
This involves the combustion of colourless odourless flammable hydrogen gas and colourless odourless oxygen gas to form a colourless liquid compound water.
hydrogen + oxygen -----> water
2H2(g) + O2(g) -----> 2H2O(l)
The reaction is high exothermic (gives our large amount of heat and light).
Decomposition of compounds
The elements in a compound cannot be separated by physical separation methods because they are chemically combined, not physically mixed. However, they can break down into two or more simpler substances through chemical processes. Decomposition provides evidence that compounds are made up of two or more different elements. There are two methods to breakdown a substance: thermal decomposition using heating and electrolytic decomposition using electric current.
1. Thermal decomposition of metal oxide
heat
mercury(II) oxide -----> mercury + oxygen
heat
2HgO(s) -----> 2Hg(l) + O2(g)
The red solid mercury(II) oxide decomposes into silvery grey liquid mercury and colourless odourless oxygen gas.
2. Thermal decomposition of metal hydroxide
heat
magnesium hydroxide -----> magnesium oxide + water vapour
heat
Mg(OH)2(s) -----> MgO(s) + H2O(g)
The white solid magnesium hydroxide decomposes into white magnesium oxide an colourless odourless water vapour.
3. Thermal decomposition of metal carbonates
In general, metal carbonates decompose to form metal oxides and carbon dioxide:
heat
metal carbonate -----> metal oxide + carbon dioxide
However, some metals are known as unreactive metals and their metal oxides can easily decompose into metal and oxygen gas:
heat
metal carbonate -----> metal + carbon dioxide + oxygen
3a) thermal decomposition of copper(II) carbonate
heat
copper(II) carbonate -----> copper(II) oxide + carbon dioxide
heat
CuCO3(s) -----> CuO(s) + CO2(g)
Upon heating, green solid copper(II) carbonate decomposes into black solid copper(II) oxide and colourless odourless acidic gas, carbon dioxide, which forms a white precipitate in limewater.
3b) thermal decomposition of silver carbonate
heat
silver carbonate -----> silver + carbon dioxide + oxygen
heat
2AgCO3(s) -----> 2Ag(s) + 2CO2(g) + O2(g)
Upon heating, yellow solid silver carbonate decomposes into silvery grey solid metal silver, colourless odourless acidic gas, carbon dioxide, which forms a white precipitate in limewater, and colourless odourless neutral gas, oxygen.
You will learn more about decomposition of metal carbonates in the topic of Metals.
4. Thermal decomposition of metal nitrates
In general, metal nitrates decompose to form metal oxides, nitrogen dioxide and oxygen:
heat
metal nitrate -----> metal oxide + nitrogen dioxide + oxygen
However, some metals are known as unreactive metals and their metal oxides can easily decompose into metal and more oxygen gas:
heat
metal nitrate -----> metal + nitrogen dioxide + oxygen
4a) thermal decomposition of magnesium nitrate
heat
magnesium nitrate -----> magnesium oxide + nitrogen dioxide
heat
2Mg(NO3)2(s) -----> 2MgO(s) + 4NO2(g) + O2(g)
Upon heating, white salt magnesium nitrate decomposes white solid magnesium oxide and a brown nitrogen dioxide gas. Nitrogen dioxide is one of the main contributors to the formation of acid rain.
4b) thermal decomposition of silver nitrate
heat
silver nitrate -----> silver + nitrogen dioxide + oxygen
heat
2AgNO3(s) -----> 2Ag(s) + 2NO2(g) + O2(g)
Upon heating, white salt silver nitrate decomposes into silvery grey solid metal silver, a brown acidic nitrogen dioxide gas and colourless odourless neutral oxygen gas. Actually silver oxide is first formed but due to its being unstable to heat, it further decomposes into silver and oxygen gas.
You will learn more about decomposition of metal nitrates in the topic of Metals.
5) Electrolytic decomposition of water
electric current
water --------------------> hydrogen + oxygen
electric current
2H2O(l) --------------------> 2H2(g) + O2(g)
Using electric current, water, a colourless odourless liquid compound, is decomposed into hydrogen gas, a colourless, highly flammable neutral gas and oxygen gas, a colourless odourless gas that supports combustion (burning).
Names of compounds
1. Compounds that contains metal and non-metal elements
When the compound consists of a metal and non-metal, the name starts with the name of the metal and ends with the name of the non-metal, with the ending of the non-metal name modified to be -ide.
1a) metal and Group VI non-metal
- metal and oxygen gives metal oxide,
- metal and sulfur gives metal sulfide
- the metal is written in front, the non-metal written at the back
- Group I, II and III metal oxide are white
- Notice that each group of metal forms molecules with the non-metals with the same ratio. For example, for Group I metal, the ratio of metal to oxygen is 2:1 and the ratio of metal to sulfu is also 2:1.
| Group I metal | Group II metal | Group III metal | Group IV metal | Transition metal | |
|---|---|---|---|---|---|
| oxygen, O | lithium oxide Li2O, sodium oxide Na2O, potassium oxide K2O |
magnesium oxide MgO, calcium oxide CaO |
aluminium oxide Al2O3 | lead(II) oxide PbO, lead(IV) oxide PbO2, lead tetroxide/lead(II,IV) oxide, Pb3O4 tin(II) oxide SnO, tin(IV) oxide SnO2 |
manganese(II) oxide MnO, manganese(IV) oxide MnO2, copper(I) oxide Cu2O, copper(II) oxide CuO, iron(II) oxide FeO, iron(III) oxide Fe2O3, triiron tetraoxide/iron(II,III) oxide Fe3O4, zinc oxide ZnO |
| sulfur, S | lithium sulfide Li2S, sodium sulfide Na2S, potassium sulfide K2S | magnesium sulfide MgS, calcium sulfide CaS |
aluminium sulfide Al2S3 | lead(II) sulfide, PbS tin(IV) sulfide, SnS2 |
copper(II) sulfide, CuS iron(II) sulfide, FeS zinc sulfide, ZnS |
1b) metal combined with hydroxide (OH-) gives metal hydroxide
- the metal is written in front, the non-metal written at the back
- Group I, II, III and IV metal hydroxides listed below are white in solid state.
- zinc compounds are usually white.
- copper compounds are usually blue/green, iron(II) compounds are usually green, iron(III) compounds are usually reddish-brown
Group I metal hydroxide: lithium hydroxide LiOH sodium hydroxide NaOH, potassium hydroxide KOH
Group II metal hydroxide: magnesium hydroxide Mg(OH)2, calcium hydroxide Ca(OH)2, barium hydroxide Ba(OH)2
Group III metal oxide: aluminium hydroxide Al(OH)3
Group IV metal oxide: lead(II) hydroxide Pb(OH)2
Transition metal oxide: copper(II) hydroxide Cu(OH)2, iron(II) hydroxide Fe(OH)2, iron(III) hydroxide Fe(OH)3, zinc oxide Zn(OH)2
1c) metal and hydrogen gives metal hydride
- the metal is written in front, the non-metal written at the back
Group I metal hydrides: lithium hydride LiH, sodium hydride NaH, potassium hydride KH, rubidium hydride RbH
Group II metal hydrides: beryllium hydride BeH2, magnesium hydride MgH2, calcium hydride CaH2
Group III metal hydrides: aluminium hydride AlH3
Transition metal hydrides: copper(II) hydride CuH2, nickel(II) hydride NiH2, zinc hydride ZnH2
1d) metal and halogen (Group VII non-metal element) gives metal halide
- modify the ending of the halogen: fluorine -> fluoride, chlorine -> chloride, bromine -> bromide, iodine -> iodide
- the metal is written in front, the non-metal written at the back
- Group I, II & III metal halides are usually white.
Group I alkali metals halides
| lithium, Li | sodium, Na | potassium, K | rubidium, Rb | caesium, Cs | |
|---|---|---|---|---|---|
| fluorine, F | lithium fluoride, LiF | sodium fluoride, NaF | potassium fluoride, KF | rubidium fluoride, RbF | caesium fluoride, CsF |
| chlorine, Cl | lithium chloride, LiCl | sodium chloride, NaCl | potassium chloride, KCl | rubidium chloride, RbCl | caesium chloride, CsCl |
| bromine, Br | lithium bromide, LiBr | sodium bromide, NaBr | potassium bromide, KBr | rubidium bromide, RbBr | caesium bromide, CsBr |
| iodine, I | lithium iodide, LiI | sodium iodide, NaI | potassium iodide, KI | rubidium iodide, RbI | caesium iodide, CsI |
Group II alkaline earth metal halides
| beryllium, Be | magnesium, Mg | calcium, Ca | strontium, Sr | barium, Ba | |
|---|---|---|---|---|---|
| fluorine, F | beryllium fluoride, BeF2 | magnesium fluoride, MgF2 | calcium fluoride, CaF2 | strontium fluoride, SrF2 | barium fluoride, BaF2 |
| chlorine, Cl | beryllium chloride, BeCl2 | magnesium chloride, MgCl2 | calcium chloride, CaCl2 | strontium chloride, SrCl2 | barium chloride, BaCl2 |
| bromine, Br | beryllium bromide, BeBr2 | magnesium bromide, MgBr2 | calcium bromide, CaBr2 | strontium bromide, SrBr2 | barium bromide, BaBr2 |
| iodine, I | beryllium iodide, BeI2 | magnesium iodide, MgI2 | calcium iodide, CaI2 | strontium iodide, SrI2 | barium iodide, BaI2 |
Group III metal halides
| aluminium, Al | gallium, Mg | indium, In | thallium, Tl | |
|---|---|---|---|---|
| fluorine, F | aluminium trifluoride, AlF3 | gallium trifluoride, gallium(III) fluoride GaF3 |
indium trifluoride, indium(III) fluoride InF3 |
thallium trifluoride, thallium(III) fluoride, TlF3 |
| chlorine, Cl | aluminium trichloride, AlCl3 | gallium trichloride, gallium(III) chloride, GaCl3 |
indium trichloride, indium(III) chloride, InCl3 |
thallium trichloride, thallium(III) chloride, TlCl3 |
| bromine, Br | aluminium tribromide, AlBr3 | gallium tribromide, gallium(III) bromide, GaBr3 |
indium tribromide, indium(III) bromide, InBr3 |
thallium tribromide, thallium(III) bromide, TlBr3 |
| iodine, I | aluminium triiodide, AlI3 | gallium triiodide, gallium(III) iodide, GaI3 |
indium triiodide, indium(III) iodide, InI3 |
- |
Group IV metal halides
- lead(II) chloride is white
- lead(II) iodide is bright yellow
| tin, Sn | lead, Pb | |
|---|---|---|
| fluorine, F | tin(II) fluoride, SnF2 tin(IV) fluoride, SnF4/ |
lead(II) fluoride, PbF2 lead(IV) fluoride, PbF4 |
| chlorine, Cl | tin(II) chloride, SnCl2 tin(IV) chloride, SnCl4 |
lead(II) chloride, PbCl2 lead(IV) chloride, PbCl4 |
| bromine, Br | tin(II) bromide, SnBr2 tin(IV) bromide, SnBr4 |
lead(II) bromide, PbBr2 lead(IV) bromide, PbBr4 |
| iodine, I | tin(II) iodide, SnI2 tin(IV) iodide, SnI4 |
lead(II) iodide, PbI2 lead(IV) iodide, PbI4 |
Some transition metal halides
- silver chloride is white, silver bromide is pale yellow, silver iodide is bright yellow, reflecting the darkening colours of halogens down its group
- iron(II) compounds are usually green; iron(III) compounds are usually yellow or reddish-brown
- copper(II) compounds are usually blue, green, or bluish-green
- nickel(II) compounds are usually green
- zinc compounds are usually white
| iron, Fe | nickel, Ni | copper, Cu | zinc, Zn | silver, Ag | mercury, Hg | |
|---|---|---|---|---|---|---|
| fluorine, F | iron(II) fluoride, FeF2 iron(III) fluoride, FeF3 |
nickel(II) fluoride, NiF2 | copper(I) fluoride, CuF, copper(II) fluoride, CuF2 |
zinc fluoride, ZnF2 | silver fluoride, AgF | mercury(I) fluoride, Hg2F2 mercury(II) fluoride, HgF2 |
| chlorine, Cl | iron(II) chloride, FeCl2 iron(III) chloride, FeCl3 |
nickel(II) chloride, NiCl2 | copper(I) chloride, CuCl, copper(II) chloride, CuCl2 |
zinc chloride, ZnCl2 | silver chloride, AgCl | mercury(I) chloride, Hg2Cl2 mercury(II) chloride, HgCl2 |
| bromine, Br | iron(II) bromide, FeBr2 iron(III) bromide, FeBr3 |
nickel(II) bromide, NiBr2 | copper(I) bromide, CuBr, copper(II) bromide, CuBr2 |
zinc bromide, ZnBr2 | silver bromide, AgBr | mercury(I) bromide, Hg2Br2 mercury(II) bromide, HgBr2 |
| iodine, I | iron(II) iodide, FeI2 iron(III) iodide, FeI3 |
nickel(II) iodide, NiI2 | copper(I) iodide, CuI, copper(II) iodide, CuI2 |
zinc iodide, ZnI2 | silver iodide, AgI | mercury(I) iodide, Hg2Cl2 mercury(II) iodide, HgI2 |
1e) metal and some polyatomic ions
- polyatomic ions are group of atoms with excess positive or negative charges
- some common polyatomic ions: carbonates, hydrogencarbonates (bicarbonates), hydroxides (already covered in 1b), sulfates, hydrogensulfates, sulfites, nitrates and nitrites
- the metal is written in front, the polyatomic group is written at the back
- Group I, II, and III compounds are usually white
- lead(II) compounds and zinc (solid) are usually white
- copper(II) compounds are usually blue, green or bluish-green
| Group I metal | Group II metal | Group III metal | Group IV metal | Transition metal | |
|---|---|---|---|---|---|
| carbonate, CO32- | lithium carbonate, Li2CO3, sodium carbonate, Na2CO3, potassium carbonate, K2CO3 |
magnesium carbonate, MgCO3 calcium carbonate, CaCO3 |
- | lead(II) carbonate, PbCO3 | iron(II) carbonate FeCO3, iron(III) carbonate, Fe2(CO3)3 copper(II) carbonate, CuCO3 zinc carbonate, ZnCO3 silver carbonate, Ag2CO3 |
| hydrogencarbonate, HCO3- |
lithium hydrocarbonate, LiHCO3, sodium hydrogencarbonate, NaHCO3 potassium hydrogencarbonate, KHCO3 |
- | - | - | iron(II) hydrogencarbonate, Fe(HCO3)2 |
| nitrate, NO3- | lithium nitrate, LiNO3 sodium nitrate, NaNO3 potassium nitrate, KNO3 | magnesium nitrate, Mg(NO3)2, calcium nitrate, Ca(NO3)2 |
aluminium nitrate, Al(NO3)3 | tin(IV) nitrate, Sn(NO3)4 lead(II) nitrate, Pb(NO3)2 | iron(II) nitrate, Fe(NO3)2 iron(III) nitrate, Fe(NO3)3 copper(II) nitrate, Cu(NO3)2 zinc nitrate, Zn(NO3)2 silver nitrate, AgNO3 |
| nitrite, NO2- | lithium nitrite, LiNO2 sodium nitrite, NaNO2 potassium nitrite, KNO2 |
calcium nitrite, Ca(NO2)2 | - | - | zinc nitrite, Zn(NO2)2 |
| sulfate, SO42- | lithium sulfate, Li2SO4 sodium sulfate, Na2SO4 potassium sulfate, K2SO4 |
magnesium sulfate, MgSO4 calcium sulfate, CaSO4 barium sulfate, BaSO4 |
aluminium sulfate, Al2(SO4)3 | tin(II) sulfate, SnSO4 lead(II) sulfate, PbSO4 |
iron(II) sulfate, FeSO4 iron(III) sulfate, Fe2(SO4)3 copper(II) sulfate, CuSO4 zinc sulfate, ZnSO4 silver sulfate, Ag2SO4 |
| hydrogensulfate, HSO4- | lithium hydrogensulfate, LiHSO4 sodium hydrogensulfate, NaHSO4 potassium hydrogensulfate, KHSO4 |
calcium hydrogensulfate, Ca(HSO4)2 barium hydrogensulfate, Ba(HSO4)2 |
- | - | - |
| sulfite, SO32- |
lithium sulfite, Li2SO3 sodium sulfite, Na2SO3 potassium sulfite, K2SO3 | - | - | - | zinc sulfite, ZnSO3 |
| silicate, SiO32- | lithium silicate, Li2SiO3 sodium silicate, Na2SiO3 potassium silicate, K2SiO3 |
magnesium silicate, MgSiO3 calcium silicate, CaSiO3 | aluminium silicate, Al2(SiO3)3 | copper(II) silicate, CuSiO3 |
Notes
i) For polyatomic ions with higher number of O atoms, the names end with -ate; lower number of O atoms ends with -ite:
- NO3-, nitrate
- NO2-, nitrite
- SO42-, sulfate
- SO32-, sulfite
- CO32-, carbonate
iii) Hydrogensulfate is also known as bisulfate. For example, sodium hydrogensulfate can be called sodium bisulfate.
2. Systematic name and common name
| molecular formula | systematic name | common name |
|---|---|---|
| Cu2O | copper(I) oxide | *cuprous oxide |
| CuCl2 | copper(II) oxide | **cupric oxide |
| FeCl2 | iron(II) chloride | *ferrous chloride |
| FeCl3 | iron(III) chloride | **ferric chloride |
| Hg2O | mercury(I) oxide | *mercurous oxide |
| HgO | mercury(II) oxide | **mercuric oxide |
| CaCO3 | calcium carbonate | limestone, marble |
| CaO | calcium oxide | lime |
| Ca(OH)2 | calcium hydroxide | slaked lime, limewater if aqueous |
| NaHCO3 | sodium hydrogencarbonage | soda bicarbonate |
| CH3COOH | ethanoic acid | acetic acid*** |
**metals with higher number (higher oxidation state) ends with "-ic".
***ethanoic acid is the main component of vinegar.
3. Naming of non-metal compounds
3a) prefixes
Notes
i) The ending of the second element is usually modified to "-ide".
ii) Prefixes are used to indicate the number of atoms:
- mono- for 1
- di- for 2
- tri- for 3
- tetra- for 4
- penta- for 5
- hexa- for 6
- hepta- for 7
- octa- for 8
- nona- for 9
- deca- for 10
iv) If there are two vowels of the same in row, the extra vowel is dropped. For example, CO is carbon monoxide, not carbon monooxide.
v) The more electropositive (less electronegative) element is written first, followed by the more electronegative (less electropositive) element. This is why O is usually written at the end because O is one of the most electronegative elements, alongwith nitrogen and fluorine. Being electronegative means having strong attraction for electrons. You will learn more about atoms and subatomic particles in the topic of Atomic Structure.
| molecular forumla | systematic name | common name |
|---|---|---|
| H2O | dihydrogen monoxide | water |
| CO | carbon monoxide | |
| CO2 | carbon dioxide | |
| CS2 | carbon disulfide | |
| SO2 | sulfur dioxide | |
| SO3 | sulfur trioxide | |
| N2O | dinitrogen monoxide nitrogen(I) oxie |
nitrous oxide |
| NO | nitrogen monoxide nitrogen(II) oxide |
nitric oxide |
| NO2 | nitrogen dioxide nitrogen(IV) oxide |
|
| NH3 | nitrogen trihydride | ammonia |
| PCl3 | phosphorus trichloride | |
| PCl5 | phosphorus pentachloride | |
| SiI4 | silicon tetraiodide | |
| XeF4 | xenon tetrafluoride | |
| SF6 | sulfur hexafluoride | |
| XeF6 | xenon hexafluoride |
3b) names of acids
| anion chemical formula | anion name | acid molecular formula | acid name |
|---|---|---|---|
| F- | fluoride ion | HF | hydrofluoric acid |
| Cl- | chloride ion | HCl | hydrochloric acid |
| Br- | bromide ion | HBr | hydrobromic acid |
| I- | iodide ion | HI | hydroiodic acid |
| CO32- | carbonate ion | H2CO3 | carbonic acid |
| NO2- | #nitrite ion | HNO2 | *nitrous acid |
| NO3- | ##nitrate ion | HNO3 | **nitric acid |
| SO32- | #sulfite ion | H2SO3 | *sulfurous acid |
| SO42- | ##sulfate ion | H2SO4 | **sulfuric acid |
| PO43- | ##phosphate ion | H3PO4 | **phosphoric acid |
| CH3COO- | ethanoate ion acetate ion |
CH3COOH | ethanoic acid acetate acid |
Notes
i) Ions that end with "-ite" (#), have acid names ending with "-ous" (*).
ii) Ions that end with "-ate" (##), have acid names ending with "-ic" (**).
3c) names of oxyanions and oxyacids
| anion chemical formula | anion name | acid molecular forumla | acid name |
|---|---|---|---|
| FO- or OF- | hypofluorite ion | HFO or HOF | hypofluorous acid |
| ClO- (3) | hypochlorite ion | HClO | hypochlorous acid |
| ClO2- (2) | chlorite ion | HClO2 | chlorous acid |
| ClO3- (1) | chlorate ion | HClO3 | chloric acid |
| ClO4- (4) | perchlorate ion | HClO4 | perchloric acid |
| BrO- | hypobromite ion | HBrO | hypobromous acid |
| BrO3- | bromate ion | HBrO3 | bromic acid |
| BrO4- | perbromate ion | HBrO4 | perbromic acid |
| IO- | hypoiodite ion | HIO | hypoiodous acid |
| IO3- | iodate ion | HIO3 | iodic acid |
| IO4- | periodate ion | HIO4 | periodic acid |
Notes:
i) There is not BrO2- and HBrO2 or IO2- and HIO2.
ii) This section is an extension of what you learned in the section just above in the naming of acids.
- ions that end with -ate, have acid names ending with -ic. See (1) chlorate ion and chloric acid.
- ions that have one fewer O atom than the ions ending with -ate, will end with -ite, and have acid names ending with -ous. See (2) chlorite ion and chlorous acid.
- ions that have two fewer O atoms than the ions ending with -ate, will have a prefix hypo- and end with -ite, and have acid names starting with hypo- and ending with -ous. See (3) hypochlorite ion and hypochlorous acid.
- ions that have one more O atom than the ions ending with -ate, will have a prefix per- and end with -ate, and have acid names starting with per- and ending with -ic. See (4) perchlorate ion and perchloric acid.
Some salts form crystals (solids with regular surfaces) that have loosely held water molecules. These are known as water of crystallisation. These water molecules can be easily removed by heating the crystals and evaporating the water molecules.
When salts have water of crystallisation, they are called hydrated salts. When these water molecules are removed, they are called anhydrous salts. This special property enables these salts to be used as a test for the presence of water.
| molecular formula | salt name | colour |
|---|---|---|
| CuSO4 | anhydrous copper(II) sulfate | white |
| CuSO4.5H2O (each unit of CuSO4 contains 5 water molecules) |
hydrated copper(II) sulfate, or copper(II) sulfate pentahydrate |
blue |
| CoCl2 | anhydrous cobalt(II) chloride | blue |
| CoCl2.6H2O | hydrated cobalt(II) chloride, or cobalt(II) chloride hexahydrate |
pink |
| FeSO4 | anhydrous iron(II) sulfate | white |
| FeSO4.7H2O | hydrated iron(II) sulfate, or iron(II) sulfate heptahydrate |
blue-green |
| Fe2O3.xH2O (the number of water molecules varies) |
hydrated iron(III) oxide (rust) | reddish-brown |
Notes
i) Cobalt(II) chloride is often available in the form of cobalt(II) chloride paper. In the dry form, it is light blue paper strip. When exposed to the air, the water vapour in the air slowly turns it into pink.
3e) names of some organic compounds
| Name | Molecular formula | Model |
|---|---|---|
| methane | CH4 |  |
| ethane | C2H6 |  |
| propane | C3H8 |  |
| butane | C4H10 |  |
| ethene | C2H4 |  |
| propene | C3H6 |  |
| butene | C4H8 |  |
| methanol | CH3OH |  |
| ethanol | C2H5OH |  |
| propanol | C3H7OH |  |
| butanol | C4H9OH |  |
| methanoic acid | HCOOH |  |
| ethanoic acid | CH3COOH |  |
| chloromethane | CH3Cl |  |
| dichloromethane | CH2Cl2 |  |
| trichloromethane / chloroform |
CHCl3 |  |
| tetrachloromethane / carbon tetrachloride |
CCl4 |  |
| diflurodichloromethane (also known as Freon-12, a type of CFCs* that is banned) |
CF2Cl2 |  |
| tetrafluroethane | CF3CH2F |  |
| propane-1,2,3-triol / glycerol |
CH2OH-CHOH-CH2OH |  |
| urea | H2NCONH2 |  |
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4) Colours of substances (elements and compounds)
If you have gone through many of the compounds above, you would have seen we have tried to highlight the colours of compounds as many as we can. Here, we consolidate them into a single table for your quick review.
| silvery grey Almost all metals e.g. Group I, II, III, IV metals, most transition and lanthanide metals | shiny yellow gold brass (copper + zinc alloy) | pinkish brown copper metal | dark brown bronze (copper + tin alloy) |
| white solid All group I, II, III and IV metal carbonates, sulfates, nitrates, and chlorides e,g, sodium carbonate, magnesium chloride, aluminium chloride, lead(II) carbonate all zinc compounds those can dissolve in water form colourless solutions | copper metal (pinkish brown) copper(II) carbonate (green) hydrated copper(II) sulfate (blue) anhydrous copper(II) sulfate (white) copper(II) hydroxide (light blue) copper(II) chloride (bluish-green) copper(II) oxide (black) copper(I) oxide (red) | iron metal (silvery grey) iron(II) oxide (black) iron(III) oxide (reddish-brown) iron(II) hydroxide (dirty green) iron(III) hydroxide (reddish brown) iron(II) carbonate / chloride / sulfate / nitrate (green) iron(III) carbonate (reddish-brown) iron(III) chloride / sulfate / nitrate (yellow) | colours of transition metal compounds manganese(IV) oxide (black) vanadium(V) oxide (yellow/brown) titanium(IV) oxide (white) potassium dichromate(VI) (orange) chomium(3+) ions (green) potassium manganate(VII) (purple) manganate(2+) ion (colourless/very pale pink) nickel (2+) ions (green) anhydrous cobalt(II) chloride (blue) hydrated cobalt(II) chloride (pink) |
| colourless gases all Group 0 noble gases e.g. helium, neon, argon, water vapour, hydrogen, oxygen, carbon dioxide, sulfur dioxide, sulfur trioxide, ammonia, all hydrocarbon gases such as methane and ethene) | coloured gases fluorine gas (yellow) chlorine gas (yellowish green) iodine vapour (purple) nitrogen dioxide (brown) | colour Group VII halogens fluorine gas (yellow) chlorine gas (yellowish green) bromine liquid (reddish brown) iodine (purple-black solid, violet vapour) | colour of iodine iodine solid (purple-black) iodine vapour (purple) iodine in hexane / chloroform (purple) iodine in ethanol (brown) iodine + potassium iodide mixture (brown) iodine-starch complex (blue-black) lead(II) iodide (bright yellow) silver iodide (bright yellow) |
| colours of Group VII halide salt with silver and lead silver chloride (white) silver bromide (pale yellow) silver iodide (bright yellow) lead(II) fluoride (white) lead(II) chloride (white) lead(II) bromide (white) lead(II) iodide (bright yellow) | colourless solutions common mineral (inorganic) acids e.g. hydrochloric acid, nitric acid, sulfuric acid, phosphoric(V) acid | white solid Group I, II, III metal oxide and metal hydroxide e.g. sodium oxide, sodium hydroxide, calcium oxide, calcium hydroxide, magnesium oxide, magnesium hydroxide, aluminium oxide aluminium hydroxide | hot and cold colours hot zinc oxide cold zinc oxide (yellow when hot, white when cold) |
| non-metal solid sulfur (yellow) diamond (colourless) graphite (black) |
Mixtures
Elements and compounds are pure substances. Mixtures are impure substances.
A mixtures is made of two or more different substances that are physically mixed but not chemically combined.As a result, a mixture retains all the properties of its constituent substances. The substances can be mixed in any composition. The constituent substances can also be separated by physical separation methods such as filtration, magnetic attraction, crystallisation, centrifugation, distillation, chromatography and separating funnel. You will learn about these in the topic of Methods of Purification and Physical Separation Techniques.
You have already learnt how to obtain a pure, dry sample of gas in Preparing, Drying and Collecting Gases. In the topic of Methods of Purification and Physical Separation Techniques, you will learn more about separating substances in solid, liquids and gaseous states.
Mixtures are more abundant in our daily lives than you can imagine. The milk, latte, coffee, fresh orange juice, blood, urine, soup, puddings, shampoos, soaps, toothpaste, dishwashing liquids, the air that you breathe, and many more are mixtures.
Types of mixtures
There are two types of mixtures: (i) homogeneous mixtures and (ii) heterogeneous mixtures
1. Properties of homogeneous mixtures (solutions)
- Uniform appearance and composition
- Allows visible light to pass through completely
- Also known as solution: solution is made up of solute dissolving in a solvent. This process is called dissolution. The solute is in a smaller amount (less than 50%) while the solvent is in a larger amount. Solute + Solvent -----> Solution
- Solute particles are very small, and cannot be seen by the naked eyes.
- Examples: salt solution, sugar solution, vinegar, perfume
- Non-uniform appearance and composition
- Does not allow light to pass through completely
- Also known as suspensions
- Particles are larger in sizes and can be seen by the naked eyes. They settle at the bottom upon resting.
- Examples: drain water, salad dressing, sand in seawater, fresh orange juice with pulp
Colloids
A colloid is a type of mixture between a homogeneous and a heterogeneous mixture. Particle sizes are between that of a homogeneous and a heterogeneous mixture. Some examples are milk, whipping cream, mayonnaise, jellies and gelatin.Concentration of solutions
In describing the concentrations of solutions, there are 3 terms: i) dilute, ii) concentrated, and iii) saturated. There are no specific numbers for whether a solution is diluted of concentrated. Generally,
- when there is much more solvent than solute (solvent > solute), the solution is diluted. For example, when you eat certain food and you find the taste is too bland.
- when there is much more solute than solvent (solute > solvent), the solution is concentrated. For example, when you eat certain food and you find it too salty or too sweet.
- when the maximum amount of solute has dissolved in a particular amount of solvent at a fixed temperature, a saturated solution is obtained.
A solution that is formed when a fixed amount of solvent contains more solute that it can normally dissolve at a particular temperature and pressure.
Solubility curve
- The solvent is usually water. After dissolving, the solid solute will be in aqueous state.
- There are also organic solvents: hexane, ethanone, methanol, ethanol, benzene
From the graph, observe that:
i) The horizontal axis shows the temperature of the solution and the vertical axis shows the maximum amount of solute that can dissolve in 100g of water at a particular temperature. Therefore, solubility curves shows the amount of solute required to produce a saturated solution.
ii) Only one substance has an almost horizontal line, sodium chloride (NaCl). This means increasing temperature has no effect on the solubility of NaCl.
iii) For most substances, increasing the temperature of the solution increase the maximum amount of solute that can be dissolved. This is to say, solubility increases as temperature increases.
iv) Put in another way, for most substances, solubility decreases as temperature decreases. This means the solution will enter into a supersaturation state when temperature starts to fall because it will contain more solute than it normally can dissolve.
v) What happens when a saturated solution starts to cool? For example, sodium nitrate (NaNO3) has a solubility of 130g per 100g H2O at 65°C. However, when it cools to 35°C, its solubility drops to 100g per 100g H2O. This means that at 35°C, only 100g can be dissolved. What will happen to the excess 30g that can no longer be dissolved? They will crystallise and reappear as solid crystals, since they are no longer soluble at the lower temperature. This is the basis of crystallisation, a physical separation method you will learn in the topic of Methods of Purification and Physical Separation Techniques.
Factors affecting solubility (the amount of solute that can be dissolved)
i) nature of solute
Certain substances dissolve in a particular solvent but not another. For example, iodine does not dissolve int water but dissolves very well in organic solvents such as chloroform (trichloromethane), hexane and ethanol to form a purple solution.
ii) nature of solvent
As explained in the nature of solute, certain substances dissolve in a particular solvent but not another.
iii) temperature
At higher temperatures, solvent particles vibrate and move more vigorously. There are more spaces between the solvent particles to accommodate more solute particles.
Factors affecting the rate of dissolving (how fast the solute can dissolve)
i) temperature
Higher temperature cause the solute and solvent particles to move faster due to higher kinetic energy. This speeds up the mixing of solute and solvent particles.
ii) stirring
Stirring helps to expose the solute particles to more solvent particles and speeds up the mixing of solute and solvent particles.
iii) particle size
The smaller the particle size, the larger the surface area exposed for solvent particles to separate solute particles and distribute them evenly throughout the solvent.
Composition of mixtures
Mixtures can be made up of:
(i) two or more different elements (a mixture of elements)
(ii) two or more different compounds (a mixtures of compounds)
(iii) two or more different elements AND compounds (a mixture of elements and compounds)
Mixtures can be made up of substances in different states:
| solute (less than 50%) |
solvent (more than 50%) |
examples |
|---|---|---|
| gas | liquid | 1) carbonated drinks, e.g. champagne, soda, coca-cola, pepsi 2) oxygen dissolved in water 3) nitrogen dioxide and sulfur dioxide dissolved in rain, forming acid rain |
| liquid | liquid | 1) alcohol-water, e.g.. beer, wine and spirits 2) acetic acid-water, i.e. vinegar |
| solid | liquid | 1) sugar-water, i.e.sugar solution 2) salt-water, i.e. salt solution |
| gas | solid | hydrogen in platinum or palladium |
| liquid | solid | mercury-another metal, e.g. silver amalgam (Hg/Ag) where liquid mercury Hg is dissolved in silver Ag |
| solid | solid | metal alloy, e.g. mild steel, stainless steel, bronze, brass, pewter, solder, duralumin |
| solid | gas | smog |
| liquid | gas | water in air |
| gas | gas | air, i.e. oxygen, carbon dioxide, water vapour and other trace amount of gases dissolving in nitrogen |
Alloys
An alloy is a mixture of a metal and small amounts of other elements.Alloys are usually produced to derive more desirable properties:
- Metals in their pure form are often too soft for practical purposes. Impurities/additives are added to increase their strength.
- Some metals corrode easily when exposed to air and water. For example, iron rusts easily when exposed to air and water, and even more so when exposed to salt water. Some impurities increase the corrosion resistance of the main metal. For example, chromium and nickel are being added to steel to make stainless steel that do not rust.
- Some alloys are used to lower the melting point so that processes can be carried at lower temperatures to save costs.
You will learn more about alloys in the topic of Metals.
Examples of alloys
| Alloy | Composition (% by mass) | Properties and Uses |
|---|---|---|
| Cast iron | iron, carbon (4%) | brittle, strong, hard, wear resistance, can rust: use in machine parts, bridge construction, cast iron cooking pans |
| High carbon steel | iron, carbon (2-3%) | strong, hard, wear resistance, can rust: rail steel, chisel, saw blades, pneumatic drills, gear wheels, springs |
| Mild steel / low carbon steel | iron, carbon (0.3-1.5%) | more ductile and malleable than other high carbon steel can rust: car bodies, nails, fences |
| Stainless steel | iron, carbon, chromium (18%), nickel (8%) | resistance to corrosion, does not rust: kitchen equipment, cutlery, stationery such as scissors, surgical instruments |
| Brass | copper (70%), zinc (30%) | resistance to corrosion, strong, attractive gold-like colour: electrical contacts of electric plugs, brass musical instruments, locks, gears, zippers, hinges, doorknobs |
| Bronze | copper (80%), tin (20%) | resistance to salt water corrosion, strong and hard, good electrical conductivity: sculptures, electrical connectors |
| Aluminium-copper alloy (use to be called duralumin) |
aluminium (94%), copper, magnesium, manganese | strong, resistance to corrosion, malleable and ductile, lightweight: car bodies, aircraft parts |
| Solder | tin (50%), lead (50%) | low melting point, good electrical conductivity: used to weld pieces of metals together, in electrical and electronics industry to to join wires and electrical contacts together |
| Pewter | tin (85-95%), copper, antimony, bismuth | low melting point, malleable: for decorative items and tableware such as dishes and jugs |
Air
Air is generally composed of 78% nitrogen (N2), 21% oxygen (O2), 0.03% carbon dioxide (CO2), 0.97% water vapour (H2O) and other noble gases such as argon (Ar), neon (Ne) and helium (He) (in decreasing concentration).
Air in city areas and polluted air are lower in oxygen and higher in carbon dioxide because of the burning of petrol in motor vehicles which uses up oxygen and produces carbon dioxide, and lower density of plants which reduces the amount of oxygen being produced.
Inhaled air and exhaled air also differs in composition:
| Inhaled air | Exhaled air |
|---|---|
| nitrogen, N2 (78%) | nitrogen, N2 (78%) |
| oxygen, O2 (21%) | oxygen, O2 (16%) |
| carbon dioxide, CO2 (0.03%%) | carbon dioxide, CO2 (4%) |
| variable, usually not saturated | saturated |
You will learn more about air in the topic of Methods of Purification and Physical Separation Techniques and in Air and the Environment.
Petroleum
Petroleum is a mixture of hydrocarbons, compounds which contain hydrogen and carbon only.
| Petroleum fractions | Boiling points (C) | Number of carbon atoms per molecule |
|---|---|---|
| Petroleum gas | below 40 | 1-4 |
| Petrol/gasoline | 40 - 75 | 5-10 |
| Naphtha | 75 - 150 | 7 - 14 |
| Kerosene/paraffin | 160 - 250 | 11 - 16 |
| Diesel oil | 250 - 300 | 16 - 20 |
| Lubricating oil/wax | 300 - 350 | 20 - 35 |
| Bitumen | above 350 | more than 70 |
A mixture of mixtures: petroleum is a mixture of many different hydrocarbon molecules and they are separated into various fractions through fractional distillation, a type of physical separation method that make use of boiling and condensation. Even after separation, each fraction is still a mixture containing different hydrocarbons that have different numbers of carbon atoms. The boiling points are not fixed and span a range of temperatures, indicating that each fraction does not consist of a pure substance but is instead a mixture.
You will learn more about petroleum in the topic of Introduction to Organic Chemistry.
Comparing compounds and mixtures
| Compounds | Mixtures |
|---|---|
| A chemical reaction takes place when a compound is formed. | No chemical reaction takes place. No new compounds are formed. |
| Constituent elements can only be separated using chemical reactions. | Constituent substances can be separated by physical separation methods. |
| Elements are always present in fixed proportion by mass. | Constituent substances vary in proportions. |
| Chemical properties are different from that of the constituent elements. | Chemical properties are the same as that of all the constituent substances. |
| Melting and boiling points are fixed. | Melting and boiling points can vary according to composition.* |
| Formation usually involves heat gain from or heat loss to the surroundings. | May involve heat gain or heat loss with the surroundings.** |
**When ammonium salts are dissolved such as ammonium chloride or ammonium nitrate, heat is absorbed from the surroundings by the reaction, causing the container to cool down and becomes cold. You will learn more about this in the topic of Energy from Chemicals.
Summary
- Definition of atoms and molecules
- Physical and chemical properties of substances
- Definition of elements, three types of elements and their properties: metals, non-metals and metalloids, and the Periodic Table of Elements, properties and uses of elements
- Elements exists as single atoms or molecuels
- Definition of compounds, synthesis and decomposition of compounds, naming of compounds, properties and uses of compounds, colour of compounds
- Definition of mixtures, types of mixtures according to different perspectives, uses of mixtures, separation of mixtures, differences between compounds and mixtures
Mindmap
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