Question
Distinguish clearly between salt-like and covalent hydrides.
✓
Answer
Salt-like hydrides are also called ionic hydrides. They are formed by group 1 and 2 elements with $\mathrm{H}_2$. They are basic in nature. They dissolve in water forming alkali and give $\mathrm{H}_2$ gas, e.g., $\mathrm{NaH}, \mathrm{CaH}_2, \mathrm{KH}$, etc.
$\mathrm{NaH}+\mathrm{H}_2 \mathrm{O} \longrightarrow \mathrm{NaOH}+\mathrm{H}_2$
Covalent hydrides are formed between less electropositive or electronegative elements, e.g., $\mathrm{B}_2 \mathrm{H}_6 \mathrm{~AlH}_3, \mathrm{BeH}_2$ etc. They are insoluble in water.
$\mathrm{NaH}+\mathrm{H}_2 \mathrm{O} \longrightarrow \mathrm{NaOH}+\mathrm{H}_2$
Covalent hydrides are formed between less electropositive or electronegative elements, e.g., $\mathrm{B}_2 \mathrm{H}_6 \mathrm{~AlH}_3, \mathrm{BeH}_2$ etc. They are insoluble in water.
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