Ionisation energy

First ionisation energy definition

The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous ions

Factors affecting ionisation energy

Atomic radius

Nuclear charge

Electron shielding

second ionization energy

Is greater than first. This is because the ratio of protons to electrons has increased

First ionisation energy equation

X(g) -> X+(g) + e-

Trends in first ionisation energy down a group

Atomic Radius Increases.

Shielding from electron shells increases - more inner shells. So despite an increase in nuclear charge.

Nuclear Attraction decreases and less energy is required to remove an electron.

Trends in first ionisation energy across a period

Nuclear Charge increases. Electrons are removed from same Shell with similar shielding.

Nuclear Attraction Increases

Atomic Radius decreases so kore energy is required to remove an electron.

Therefore First Ionisation Energy increases