Hydrogen reacts with metals or non metals to form binary compounds known as hydrides.

Hydrides are mainly classified into the following 3 types: 

1. Ionic or salt like hydrides

These are stoichiometric compounds of dihydrogen formed with most of the s-block elements which are highly electropositive in character. These are crystalline, non-volatile and non-conducting in solid state. But their melts conduct electricity and on electrolysis liberate dihydrogen gas at anode. They react violently with water producing dihydrogen gas. 

e.g. NaH, KH.

2. Covalent hydrides or Molecular hydrides

These are formed by the action between dihydrogen and non metals (p-block elements). Covalent hydrides are classified into electron-deficient (e.g. B₂H₆), electron-precise (e.g. CH₄) and electron-rich hydrides (e.g. NH₃).

3. Metallic or Non-stoichiometric or Interstitial hydrides 

These are formed by the reaction of dihydrogen with many d-block and f-block elements. These hydrides conduct heat and electricity. They are almost always nonstoichiometric, being deficient in hydrogen,

e.g. LaH_2.87 ,YbH_2.55 ,VH_0.56 etc.