Trends in Properties (Oxford AQA International A Level Chemistry)

Group 7 elements are known as the halogens

The elements are:

• Fluorine

• Chlorine

• Bromine

• Iodine

• Astatine

Electronegativity is the ability of an atom to attract electrons to itself in a covalent bond

Going down Group 7, electronegativity decreases because:

• The atomic radii of the elements increases

• The outer shell gets further away from the nucleus so there is more shielding by inner shell electrons

• The incoming electrons are further away from the positive nucleus so there is less attraction between them

• The increased shielding outweighs the effect of the increasing nuclear charge down the group

Going down Group 7, the state of the halogens at room temperature changes:

• Fluorine and chlorine are gases

• Bromine is a liquid

• Iodine and astatine are solids

Going down Group 7, the melting and boiling point of the elements increases because:

• The atoms become larger so have more electrons

• Therefore, there are stronger van der Waals' forces between the molecules

• These require more energy to overcome