Question

Name the class of the hydride to which \[{H_2}O\], \[{B_2}{H_6}\] and \[NaH\] belong?

Answer 1

Hint: Hydrogen generally forms a proton but when it binds with an element which has lower electronegativity and forms a compound. It is considered as a hydride ion. So, basically hydride refers to an anion of the hydrogen atom.

Complete answer:
Let us first understand the term hydride. A hydride refers to an anion of hydrogen. It forms basically when the hydrogen forms a compound with an element which has lesser electronegativity. Hydride has a negative \[\left( { - 1} \right)\] and it is represented as \[{H^ - }\] .
There are different types of hydride forms when the hydrogen combines with different elements.
Ionic hydride- this type of hydride is formed when hydrogen forms compounds with group II elements. Example – Potassium hydride \[(KH)\], lithium hydride \[\left( {LiH} \right)\] and sodium hydride \[(NaH)\]
Molecular hydride- this kind of hydrides are when hydrogen form compound with electron rich compound i.e. P- block elements. Example – water \[({H_2}O)\] and ammonia\[(N{H_3})\].
Interstitial hydride- This type of hydride is formed when hydrogen forms a compound with a D-block element. Example -scandium hydride \[(Sc{H_3})\] and zinc hydride \[(Zn{H_2})\].
Electron precise hydride- when the exact number of electrons form normal covalent bonds, these are termed as electron precise hydride. It is mainly formed by group \[14\] elements. Examples- methane and ethane etc.
So, in the given question:
\[NaH\] is an ionic hydride, also called as saline hydride whereas \[{H_2}O\] and \[{B_2}{H_6}\] belong to covalent hydrides or molecular hydride. \[{B_2}{H_6}\] is an electron deficient molecular hydride and \[{H_2}O\] is an electron rich hydride.

Note:
The metals of the group i.e.\[7th\], \[8th\] and \[9th\] do not form any hydride and this region is referred to as hydride gap or hydrogen gap. In electron deficient hydrides, the octet is not completed, even then the molecule will be stable.