Topic 2.6 - Electron Affinity

What is electron affinity?

The energy change on adding an electron to a gaseous atom, ion, or molecule

What does it mean when an element has a negative electron affinity?

Less energy is required to add an electron, therefore it is favourable

Why are the electron affinities of the group 1 elements negative?

By adding an electron, the s shell becomes completely filled therefore it is favourable to add an electron

Why do the group 2 elements have positive electron affinities?

Adding an electron results in the filing of a p orbital which is higher in energy, therefore more energy is required to add an electron

Why is it easier to add an electron to an atom across a p-block period?

Due to increasing effective nuclear charge

Why do group 15 elements have a lower electron affinity than those in group 14?

There is significant inter electron repulsion in the p orbital of a group 15 element when adding an electron due to adding it to a half-filled shell, therefore it is more difficult to do so

Why do F and O have lower electron affinity than expected?

Due to their small size, there is more inter electron repulsion