Ncert Exercises & Solutions

What are metallic/interstitial hydrides? How do they differ from molecular hydrides?

Metallic/interstitial hydrides are formed by many d-block and f-block elements. These hydrides conduct heat and electricity.

Unlike saline hydride, they are almost always non-stoichiometric, boing deficient in hydrogen. e.g.,

{LaH}_{2.87}

{YbH}_{2.55}

{TiH}_{1.5 - 1.8}

{ZrH}_{1.3 - 1.75}

{VH}_{0.56}

{NiH}_{0.6 - 0.7}

{PdH}_{0.6 - 0.8}

etc. In such hydrides, the law of constant composition does not hold good.

Comparison between molecular and metallic hydrides

Molecular hydrides	Metallic hydrides
These are mainly formed by p-block elements and some s-block elements (Be and Mg).	The are formed by group 3, 4, 5 (Sc, Ti, V, Y, Zr, Nb, La, Hf, Ta, Ac etc.) 10, 11, 12 (Pd, Cu, Zn etc.) and f-block elements (Ce, Eu, Yb, Th, U etc.)
Those are usually volatile compounds having low melting and boiling point	These are hard, have metallic lustre.
It conducts electricity	These do not conduct electricity.