Covalent and interstitial
Hydrogen form molecular compounds with p-block elements (B, C, N, O, F; Si, P, S, Cl; Ga, Ge, As, Sb, Br; In, Sn, Sb, Te, I; Tl, Pb, At). common examples of such hydrides are CH3, NH3, H2O, HF etc. The stability of these hydrides decreases down the group. For example, NH3 > PH3 > AsH3 > SbH3 > BiH3. In a period the stability increases with increasing electronegativity. For example, CH4 < NH3 < H2O < HF. Molecular hydrides are classified as electron rich, electron precise and electron deficient hydrides.
(a) Electron rich molecular hydrides:
These hydrides have one or more lone pairs of electrons around the central more electronegative element. For example
H — O — H, H — N — H, H — F:
(b) Electron precise molecular hydrides:
Elements of group 14 form such hydrides. The bond length increases on going down the group. A common example of electron precise molecular hydrides is CH4.
(c) Electron deficient molecular hydrides:
These hydrides have lesser number of electrons than that required for writing the conventional Lewis structure. A common example of such molecular hydride is diborane, B2H6.
(d) Systematic names of molecular hydrides:
The systematic names of these hydrides are obtained from the name of the element and the suffix –ane. For example, PH3 H2O NH3
The difference between Covalent hydrides and Interstitial hydrides:
The covalent hydrides are those hydrides which include the hydrocarbons and many other compounds which covalently bond to hydrogen atoms.
The interstitial hydrides are those hydride which may be described as having metallic bonding.
Example of Metallic Hydrides
Metal hydrides are known as interstitial hydrides. They are formed when hydrogen molecule reacts with the d- and f-block elements. The Metals of group 7, 8, and 9 do not form hydrides. Metal hydride do conduct heat and electricity but not to the extent of their parent metals.
TiH aluminium, cadmium, magnesium, etc.
Uses of Hydride
Hydrides are used as reducing agents in many chemical industries.
Hydrides are highly significant in battery storage technologies such as nickel hydride batteries.
Hydrides are used as drying agents.
Hydrides are used as strong bases in organic synthesis.
The metal hydrides are also used for their heat storage, hydrogen storage and compressors capabilities.