Electron Affinity

Key points:

Electron Affinity is the energy released when an electron is added to the outermost shell of an isolated, neutral gaseous atom.
The electron affinity increases from left to right in a period.
The electron affinity decreases down the group.

Factors affecting Electron Affinity:

The key factors that influence electron affinity are as follow:

Atomic size
Nuclear charge
Stable Electron configuration

Atomic size :

The larger the atomic size of the element in the periodic table refers to the bigger atomic radius.

The bigger atomic size is due to the increase in shell number, the electrons being far away from the nucleus will experience a lesser nuclear force of attraction.

Therefore, it will result in lesser electron affinity.

Let’s compare sodium (Na) and Chlorine(Cl) atoms, which one has more electron affinity.

As we move across period 3, the electron affinity increases due to the decreases in atomic size and the increase in nuclear charge.

Therefore, chlorine has more electron affinity than sodium.

Nuclear charge :

Effective nuclear charge (Z) is due to the number of protons in the nucleus of an atom.

The greater nuclear charge will result in a more electron affinity.

This happens because the nucleus attracts the electrons more towards itself.

nuclear charge influences electron affinity

Stable Electron Configuration :

Atoms with stable electronic configurations can make it challenging to add electrons, therefore having more electron affinity.

Now the question is what is a stable electronic configuration?

Atoms with full filled orbitals (s=2, p=6, d=10 & f=14 electrons) and half filled orbital ( s=1, p=3 , d=5 & f= 7 electrons) are stable and its too difficult to add electron in stable configuration.