Question

All alkaline earth metals combine directly with $H_2$ and form ionic hydrides as $M{H}_2$ except:

• A. $Mg$
• B. $Ca$
• C. $Be$
• D. $Sr$

Answer 1

The correct option is C $Be$

Option $\left(C\right)$ is correct.

$Be$ does not combine directly with $H_2$ but $Be{H}_2$ is prepared from preformed beryllium(II) compounds and $Be{H}_2$ is covalently bonded.

All other alkaline earth metals react directly with hydrogen to produce the binary hydrides ($M{H}_2$). The hydrides of the heavier alkaline earth metals are ionic, but $Be{H}_2$ has polymeric structures that reflect covalent character.