Question

Explain the trend of the following in group 13 elements:

electron affinity

Answer 1

1. Electron affinity shows an irregular trend. It first increases from B to Al and then decreases. The less electron affinity of boron is due to its smaller size. Adding an electron to the 2p orbital in boron leads to a greater repulsion than adding an electron to the larger 3p orbital of aluminium.
2. From Al to Tl, electron affinity decreases. This is because nuclear charge increases but simultaneously the number of shells in the atoms also increases. As a result, the effective nuclear charge decreases down the group resulting in increased atomic size, and thus, it becomes difficult to add an electron to a larger atom. The electron affinity of Ga and In is the same.