Explain the trend of the following in group 13 elements:
- 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.
- 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.
Concept: Trends in Atomic and Physical Properties of Elements of Groups 13, 14 and 15
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