Question

Why are the melting points of antimony and bismuth lower than the expected values?

Answer 1

1. They tend to form three covalent bonds rather than five because of the inert pair effect.
2. This reduces the strength of interatomic attractions.
3. Weaker interatomic forces lower the melting points.
4. Bismuth has a larger atomic size than arsenic, which further weakens its interatomic forces, resulting in an even lower melting point.

Hence, the inert pair effect and larger atomic size cause their melting points to be lower than expected.