Question

Determine the interatomic spacing for NaBr, NaCl, NaF, NaI

Use this to arrange them in order of their probable melting point.

Answer 1

The interatomic distance is the sum of the radii of the cation and teh anion.

The atomic radii for Na⁺ is 102 and that of Br^- is 196, Cl^- is 181, F^- is 133 and I^- is 220.

Therefore, the interatomic spacing for NaBr is (102+196) = 298.

The interatomic spacing for NaCl is (102+181) = 283.

The interatomic spacing for NaF is (102+133) = 235.

The interatomic spacing for NaI is (102+220) = 322.

As the atomic size of the halogen increases, the distance from the nucleus increases. As a result, melting point decreases.

The order of melting points is NaF > NaCl > NaBr > NaI.