Question

What is hydride? How many types of hydrides are there? Explain with example.

Answer 1

Hydrides:

The binary compounds of dihydrogen with other elements except noble gases are called hydrides.

Types of Hydrides

There are following types of hydrides :

1. Covalent of Molecular hydride :

Dihydrogen forms molecular hydrides with most of the p-block elements. They consist of discrete covalent molecules which are held together by weak Vander Waal’s forces of attraction. They have low melting and boiling point. They are volatile in nature
e.g., CH₄ , NH₃, H₂O and HF.
These are of three types on the basis of relative number of electrons and bonds in their Lewis structure :

(i) Electron-deficient hydride : Elements of group 13 will form electron-deficient hydrides. They act as Lewis acids, e.g., B₂H₆.

(ii) Electron-precise hydride : All elements of group 14 form electron-precise hydrides, e.g., CH₄.

(iii) Electron-rich hydride : Elements of group 15-17 form such compounds. They act as Lewis bases, e.g., NH₃.

2. Ionic or Saline hydrides:

These are stoichiometic compounds of dihydrogen formed with most of the s-block elements i.e., alkali and alkaline earth metals. These hydrides are crystalline, non-volatile and non-conducting in solid state. They have high melting and boiling points.
e.g., NaH, BeH₂, MgH₂ etc.

3. Metallic or Interstitial hydrides : 

These hydrides are formed by the reaction of dihydrogen with d-block and f-block elements. Due to small size of dihydrogen in these hydrides, hydrogen occupies interstices in the metal lattice producing distortion without any change in its type. So, these are known as interstitial hydrides. These are non-stoichiometric being deficient in hydrogen.
e.g., ScH₂, LaH₂, T₂H₂, CrH₃ etc.