A Closer Look at Ionisation Energies

There is a small drop between magnesium and aluminium. Magnesium has its outer electrons in the 3s sub shell, whereas aluminium starts to fill the 3p sub shell. Aluminium’s electrons are easier to remove because they are in a higher energy level

Aluminium has a lower first ionisation energy than magnesium because its outer electrons are in a higher energy orbital, which make them further from the nucleus and ultimately less tightly bound to the nucleus

The ionisation energy drops because sulfur (Group 6) has a paired electron in its 3p orbital, which leads to increased electron - electron repulsion, making it easier to remove an electron compared to phosphorus, where the 3p electrons are unpaired

Each successive ionisation energy is higher than the previous because it becomes increasingly harder to remove electrons, due to the increasing positive charge of the ion and the decreasing repulsion between remaining electrons

The number of electrons that are relatively easy to remove corresponds to the group number. For example, in Group 2 elements, the first two electrons are relatively easy to remove - large jump in ionisation energy occurs after second electron is removed

The sharp increase indicates that the first electron is in the outermost shell, which is much easier to remove, while second electron is from a more tightly bound shell, leading to a significantly higher ionisation energy

These values suggest that the element is in Group 2 of the Periodic Table because there is a large jump after the second electron is removed, indicating the transition from the outermost shell to a more tightly bound inner shell