Periodicity revision notes

Periodicity – the trends that occur (in physical and chemical properties) as you move across the periods.

As you move across the periodic table metals change to non-metals and solids change to gasses.

Atomic radius

·         Atomic radius decreases across a period, as the number of protons increase the charge of the nucleus becomes more positive, so electrons as pulled in slightly closer.

Ionisation energy

·         Ionisation energy increases across a period due to:

1.    Atomic radius – the further the outer shell electrons from the nucleus, the lower the ionisation energy.

2.    Nuclear charge – the more protons in the nucleus, the higher the ionisation energy.

3.    Electron shielding – the more inner shells there are, the more shielding there is, and the lower the ionisation energy.

·         Ionisation energy decreases down a group due to:

1.    Elements further down the group have more electron shells, so there is more shielding, so electrons can be removed more easily.

2.    Less attraction from the nucleus.

Melting and boiling points

·         For metals, melting and boiling points increase across the period as the metallic bonding gets stronger. This is due to metal ions having an increasing number of delocalised electrons and a decreasing ionic radius, so there is a decreasing ionic radius.

·         From group 1 to 3 there is an increase in boiling points, as there is metallic bonding – strong forces between positive metal ions and delocalised electrons

·         From group 4 there is a sharp decrease in boiling point, as there is giant covalent bonding, which are strong forces between atoms, weaker than metallic bonds.

·         From group 5 to 0 there are comparatively low boiling points, as there are van der Waals’ forces, which are weak forces between molecules.