Chemistry – Topic 4 Revision notes
C2.17: Chemical Classification
The atoms of elements in a compound are held together with chemical bonds.
The type of bonding affects the properties of the material.

Ionic bonds form when a metal reacts with a non-metal.
Covalent bonds form between atoms of non-metal elements.
Metals are good conductors of heat and electricity and are solids at room temperature.
Mercury (metal) is a liquid at room temperature.
Metals don’t dissolve in water, they are malleable (can be hammered into shape).
The atoms in metals are held together by metallic bonds.
C2.18: Metallic bonding and transition metals
All metals have only a few electrons in the outer shells of their atoms.
The atoms are close together and the outer shells overlap.
Outer electrons are free to move through the structure in a ‘sea of electrons’.
Delocalised electrons move around randomly between positive ions in all directions.
If a potential difference is applied across a piece of metal, the electrons start to drift in one direction.
Movement of electrons is electric current.
Most metals are transition metals.
These are in the centre of the periodic table.
They have high melting points and form coloured compounds.
C2.19: Alkali metals
Alkali metals are found in group 1.
Solids in room temperature but have low melting points.
Soft metals.
They are held together by metallic bonding.
They all react with water to form a metal hydroxide and hydrogen gas.
Metal hydroxides are alkaline.
The elements at the bottom of group 1 have more electrons than the ones on top.
C2.20: Halogens
Halogens have 7 electrons in their outer shell, so they all have similar properties.
At room temperature:
Chlorine is fairly reactive, poisonous, dense green gas.
Bromine is dense, poisonous, orange liquid.
Iodine is a dark grey crystalline solid.
Halogens react with metals to form metal halides.
They can react with hydrogen to form hydrogen halides.
The higher an element in group 7 is, the more reactive it is. This is because the outer shell is nearer to the nucleus, so the pull from the positive nucleus is greater which