What do you expect the nature of hydrides is, if formed by elements of atomic numbers 15, 19, 23 and 44 with dihydrogen? Compare their behaviour towards water.
The elements of atomic numbers 15, 19, 23, and 44 are nitrogen, potassium, vanadium, and ruthenium respectively.
1) Hydride of nitrogen:
Hydride of nitrogen (NH3) is a covalent molecule. This hydride molecule contains excess of electrons and hence it is electron rich hydride molecule.
2) Hydride of potassium:
This hydride is ionic in nature because of the strong electropositive nature of potassium ion and hence it is crystalline in nature.
3) Hydrides of Vanadium and Ruthenium:
d and f-block elements form non-stoichiometric hydrides and vanadium and ruthenium also belong to the d-block of the periodic table. Hydrides of vanadium and ruthenium are therefore, metallic in nature having a deficiency of hydrogen.
4) Behaviour of hydrides towards water:
Potassium hydride reacts violently with water and the reaction is given as below:
KH + H2O → KOH + H2
Ammonia (NH3) behaves as a Lewis base and the reaction of ammonia with water is given as below:
NH3 + H2O ß→ OH- + NH4+
Vanadium and ruthenium hydride do not react with water.
Hence, the increasing order of reactivity of the hydrides is:
(V, Ru) H < NH3< KH.