Question

Which of the following are true for interstitial compounds:

• A. Small atoms like Hydrogen, Boron etc. occupy the interstitial holes in a metal lattice
• B. These compounds are non-stoichiometric and cannot be decisively classified as ionic or covalent
• C. The formulae do not correspond to any normal oxidation state of the metal
• D. These compounds have the same appearance as that of the parent metal

Answer 1

Answer: (A), (B), (C)

The correct options are
A Small atoms like Hydrogen, Boron etc. occupy the interstitial holes in a metal lattice
B These compounds are non-stoichiometric and cannot be decisively classified as ionic or covalent
C The formulae do not correspond to any normal oxidation state of the metal

Atoms with small radii like H, B, C and N occupy the interstitial holes of the metals to form combinations called interstitial compounds. Examples: $V{H}_{0.56},Ti{H}_{1.7}$
Clearly, there is no fixed stoichiometric ratio for this combination. Different combinations can be achieved using different conditions like temperature and pressure. In this regard, it is impossible to classify these non-stoichiometric compounds as ionic or covalent. Further, we cannot satisfactorily assign any realistic oxidation number to the central metal atom. Also, the physical properties definitely undergo a change. So the appearance need not be the same as the parent metal.