Question

How are hydrides classified?

Answer 1

Hint: Hydrogen combines with an outsized number of other elements including metals and non-metals, except noble gases to create binary compounds called hydrides.

Complete step by step answer: If 'E' is that the symbol of the element then hydrides are represented as EH leg. BeH) or E H, (e.g.. B,H).Based on their physical and chemical properties, the hydrides are classified into three main categories:
(i)Ionic or saline or salt like hydrides
(ii) Covalent or molecular hydrides
(iii)Metallic or non-stoichiometric hydrides Ionic or Saline Hydrides: 
The ionic hydrides are stoichiometric which are formed when hydrogen combines with elements of s-block elements except Be. Ionic hydrides are formed by transfer of electrons from metals to hydrogen atoms and contain hydrogen as H ion eg., hydride (NaH), hydride etc. a number of the properties of saline hydrides are as follows:
1. These are white crystalline solids and have ionic lattices and behave like salts.
2. They have high melting and boiling points 
3. These are non-volatile and non-conducting in solid state, however they conduct electricity in fused state liberating hydrogen at anode which confirms the existence of H ion.
4. These hydrides react violently with water producing hydrogen gas.
Covalent or Molecular Hydrides:
Covalent or molecular hydrides are the compounds of hydrogen with p-block elements. the foremost common hydrides are etc. Covalent hydrides are volatile compounds. Molecular hydrides are further classified consistent with their relative number of electrons and bonds in their Lewis structures.
1. Electron deficient molecular hydrides:
These hydrides have a lesser number of electrons than that required for writing the traditional Lewis structure. All the hydrides of group 13 form electron deficient compounds like which polymerise to make As these are electron deficient, in order that they have an inclination to just accept the electrons, therefore, act as Lewis acids.
2. Electron-precise hydrides: Such compounds have required a number of electrons to put in writing their conventional Lewis structures. The weather of group 14 forms such hydrides. The hydrides have tetrahedral geometry.
3. Electron-rich hydrides: Electron-rich hydrides have excess electrons within the type of one or more lone pairs of electrons round the central electronegative element. Therefore, these hydrides because of the presence of lone pairs of electrons form electron-rich hydrides. In Fact the presence of lone pairs of electrons on electronegative elements leads to the association of molecules because of hydrogen bonding. These forms of hydrides are formed by elements of group 15-17 ( has 1 lone pair, has 2 lone pairs, HF has 3 lone pairs). Metallic or Non-Stoichiometric (or Interstitial) Hydrides: The elements of group 3, 4, 5 (d-block) and f-block elements form metallic hydrides. In group 6, only chromium forms hydride (CrH). Metals of group 7, 8, 9 don't form hydrides. These hydrides are called metallic hydrides because they conduct electricity. Moreover these hydrides are non-stoichiometric with variable composition, being deficient in hydrogen. So, just in case of metallic hydrides, the law of constant composition doesn't hold good.
Metallic Hydrides: The interstitial hydrides generally have properties almost like those of parent metals, they're hard, have metallic lustre, conduct electricity, and have magnetic properties. These hydrides are less dense than parent metal. There is a lot of ambiguity within the nature of bonding in non-stoichiometric transition metal hydrides. Earlier it had been thought that hydrogen occupies interstices within the metal lattice producing distortion with none change in its type. These hydrides are, therefore, sometimes called interstitial hydrides. But recent studies have disproved this fact.

Note: Transition metals have a property of adsorption of hydrogen which is employed in catalytic reduction and hydrogenation reactions. There are some metals like Palladium (Pd) and Platinum (Pt) which might absorb an outsized volume of hydrogen and so used as its storage media, especially in cars functioning on fuel cells.