CH7 periodicity

First ionisation energy

The energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions.

Second ionisation energy

The energy required to remove one electron from each ion in one mole of gaseous 1+ ions of an element to form one mole of gaseous 2+ ions.

Trend in first ionisation energies down a GROUP

Decreases because atomic radius decreases, shielding increases, nuclear attraction decreases.

Trend in first ionisation energy across a PERIOD

Increases because nuclear charge increases, similar shielding, nuclear attraction increases, atomic radius decreases.

Metallic bonding

The strong electrostatic attraction between cations and delocalised electrons