Why are interstitial compounds well known for transition elements ?

Explanation

The compounds formed when small atoms like H, C or N get trapped inside the crystal lattice of metals are known as interstitial compounds. A number of interstitial compounds are formed by the transition metals. Transition metals react elements such as hydrogen, carbon, nitrogen, boron etc., to form interstitial compounds. Transition metals have crystals which are either hexagonal close-packed or face-centred cubic structures. Both of these lattices are very similar and have two type of holes. Firstly, there can be two tetrahedral holes per metal atom i.e., there is a hole between four metal atoms. Secondly, there can be one octahedral hole per atom i.e., the hole is between six metal atoms. Therefore transition metals can easily react with C, H or N and trap them inside the crystals.