Question
Sat January 26, 2013 By: Aravind Balachandran

Explain the types of covalent hydrides with examples.

Expert Reply
Sun January 27, 2013
Hydrogen forms 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). The common examples of such hydrides are CH3, NH3, H2O, HF etc. 

Covalent 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:

      ••              |               ••

                      H

(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

   Phosphane   oxidane        ozane

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