Trends in the periodic table- ionisation energy

The ionisation energy is the minimum amount of energy required to remove the most loosely bound electron from an isolated atom of an element in its ground state, and is measured in kilojoules per mole. The second ionisation is the minimum amount of energy needed to remove the second most loosely bound electron from an ion with one electron already taken

In terms of the periodic table, the ionisation energy decreases going down the group. This is due to an increasing atomic radius diminishing the attractive force of the nucleus. Also the screening effect means the attraction to the loosest electron reduces as you go down a group.

The ionisation energy increases going across a period. This is due to the increasing nuclear charge, meaning electrons are being held more firmly. As well as this the decreasing atomic radius contributes to much more pull upon the loose electrons and increases ionisation energy

Ionisation energy also depends greatly upon the stability of the electrons which is based on how full the orbitals are. A full or half full orbital will result in more stability meaning an atom is less likely to give away an electron

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