States of matter

• The particles in a solid are organised in a regular arrangement. The atoms vibrate in a fixed position and are physically touching the other atoms. These particles are low in energy.

• In a liquid, the atoms are still touching but are slightly further apart and can slide over one another. Each atom is free to move and has a moderate amount of energy.

• The atoms within a gas are arranged randomly and are far apart from one another. They are moving quickly and have a high amount of energy.

The amount of energy needed to change state from solid to liquid and from liquid to gas depends on the strength of the forces between the particles of the substance – the stronger the forces between the molecules, the more energy is needed to change its state and the higher the melting point and boiling point of the substance.

Remember that when a simple covalent molecule (such as water, ammonia or methane) changes state, it is the weak intermolecular forces between the molecules that need to break, not the strong covalent bonds that hold the atoms together.

State Symbols

There are four state symbols: solid (s), liquid (l), aqueous (aq) and gaseous (g).

• Solids – these will include most metals (except mercury) and insoluble compounds (like silver chloride and lead chloride).

• Liquid – these will include water, ethanol and molten ionic compounds.

• Aqueous – these include anything in solution e.g. sodium chloride dissolved in water

• Gaseous – elements that are gaseous at room temperature include the noble gases, fluorine, oxygen and nitrogen

Properties of ionic compounds

Ionic compounds are regular lattices made up of metals and non-metals connected by ionic bonds. Ionics compound have the following properties:

1. High melting and boiling points – due to the strong ionic bonds within the lattice which require a large amount of energy to overcome.

2. Able to conduct electricity in its aqueous or molten form  – due to the movement of charged particles (ions) when the ions are dissolved in water or melted, allowing charge to flow.

Properties of simple covalent molecules

Simple covalent molecules are molecules made up of a small number of atoms (usually non-metals). Simple covalent molecules have the following properties:

1. Low melting and boiling points – this is due to the weak intermolecular forces between molecules which break when small molecules change state (remember that the covalent bonds within the molecule stay intact).

2. Gases or liquids at room temperature – due to their low melting and boiling points

3. Unable to conduct electricity – as they are not made up of charged particles

Properties of polymers

Polymers are long chains of molecules joined together by covalent bonds. Polymers have the following properties:

1. They are made up of repeating units (monomers) joined together by covalent bonds

2. High melting and boiling points – due to the strong covalent bonds which need a lot of energy to overcome

3. Solid at room temperature – due to the high melting and boiling point

Properties of giant covalent molecules

Giant covalent molecules are huge structures made up of atoms (non-metals) joined by covalent bonds. Examples include diamond, graphite (both made of carbon) and silicon dioxide (silica). They have the following properties:

1. High melting and boiling point – due to the strong covalent bonds which need a lot of energy to overcome

2. Unable to conduct electricity – as they do not contain moving charged particles. The exception is graphite, which only forms three bonds to other carbon atoms so has an unbonded electron which becomes delocalised through its structure. The delocalise electron enables graphite to conduct electricity.

Properties of metals and alloys

Metals have certain properties which make them useful for things like frying pans, electrical power cables and car parts. In general, metals have a high melting point, conduct heat and electricity, have a high density and are malleable, which means they can be bent and hammered into shape without shattering. A brittle substance will break easily when bent. However there are a few exceptions:

• Mercury is a metal and has a low boiling point so it exists as a liquid at room temperature

• Graphite is a form of carbon, a non-metal, but can conduct electricity because it contains delocalised electrons

An alloy is a mixture of two or more elements, where at least one element is a metal. Pure metals are arranged in a regular lattice where layers can slide over one another. The more difficult it is for the layers to move, the stronger the metal.

Different elements have different sized atoms so when you mix another element with a metal it disrupts the regular arrangement of atoms. The atoms are no longer aligned in neat rows which can easily slide over each other. This makes alloys much stronger and harder than pure metals.

Metals as conductors

Anything that is charged and free to move is capable of conducting electricity. Within metals there are electrons which are free to move throughout the structure and carry a charge – these are known as delocalised electrons. Metals are good conductors of heat and electricity because energy is transferred through the metals by the delocalised electrons.

Next Page: Structure and Bonding of Carbon