Question

Which hydride among the following is less stable?

• A. BeH\(_2\)
• B. NH\(_3\)
• C. HF
• D. LiH

Hint:

Stability of hydrides in a period generally increases from left to right as the electronegativity of the element increases and the bond becomes more covalent/stable.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The stability of hydrides generally depends on the electronegativity difference, the nature of the bond (ionic vs covalent), and the bond dissociation energy.

Step 2: Detailed Explanation:
1. HF and NH\(_3\): These are covalent hydrides of highly electronegative p-block elements. They are quite stable due to strong covalent bonding and, in the case of HF, significant ionic character. 2. LiH: This is a saline (ionic) hydride. While reactive, it is thermally stable compared to Group 2 hydrides. 3. BeH\(_2\): Beryllium hydride is an electron-deficient polymer. Because Beryllium is very small and has a high polarization power, its hydride is not a simple molecule but forms a complex bridged structure to gain stability. Among the choices, it has the lowest thermal stability and is the least stable in terms of standard formation.

Step 3: Final Answer
BeH\(_2\) is the least stable among the given hydrides.