Question

What do you understand about the term non-stoichiometric hydrides? Do you expect this type of hydride to be formed by alkali metals? Justify your answer.

Answer 1

Non-stoichiometric hydrides:

• Non-stoichiometric hydrides are also known as metallic hydrides.
• These are formed by many d-block and f-block elements. Exceptions are there in the case of group 7, 8 ,and 9 as they do not form hydrides.
• These hydrides conduct heat and electricity but not as efficiently as parent metals do.
• For example, ${\mathrm{LaH}}_{2.87}$ and ${\mathrm{YbH}}_{2.55}$.

Alkali metals do not form non-stoichiometric hydrides as these metals readily lose their valence electron and behave as strong reducing agents. Thus, they form ionic or stoichiometric hydrides.

Stoichiometric hydrides:

• “These are stoichiometric compounds of dihydrogen formed with most of the s-block elements which are highly electropositive in character.”
• Stoichiometric hydrides are also known as ionic or saline hydrides.
• Examples of Stoichiometric hydrides are ${\mathrm{LiH}}_2$ and ${\mathrm{BeH}}_2$.