Question

Identify the correct order of thermal stability of hydrides of 16 group elements from the following.

• A. \(\text{H}_2\text{S}<\text{H}_2\text{O}<\text{H}_2\text{Se}<\text{H}_2\text{Te}\)
• B. \(\text{H}_2\text{O}<\text{H}_2\text{S}<\text{H}_2\text{Se}<\text{H}_2\text{Te}\)
• C. \(\text{H}_2\text{Te}<\text{H}_2\text{Se}<\text{H}_2\text{S}<\text{H}_2\text{O}\)
• D. \(\text{H}_2\text{Se}<\text{H}_2\text{Te}<\text{H}_2\text{O}<\text{H}_2\text{S}\)

Hint:

Down the group: bond length ↑ → bond strength ↓ → stability ↓.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Thermal stability of hydrides depends on the bond dissociation enthalpy of the \(\text{M-H}\) bond. As the size of the central atom (M) increases down a group, the \(\text{M-H}\) bond length increases and the bond strength decreases.
Step 2: Key Formula or Approach:
Atomic size: \(\text{O}<\text{S}<\text{Se}<\text{Te}\).
Bond strength: \(\text{O-H}>\text{S-H}>\text{Se-H}>\text{Te-H}\).
Step 3: Detailed Explanation:
Going down group 16 (\(\text{O, S, Se, Te, Po}\)), the atomic radius of the element increases. This leads to a longer and weaker bond with hydrogen. Weaker bonds are more easily broken by heat.
Therefore, thermal stability decreases down the group: \[ \text{H}_2\text{O}>\text{H}_2\text{S}>\text{H}_2\text{Se}>\text{H}_2\text{Te} \] In increasing order (as shown in C): \(\text{H}_2\text{Te}<\text{H}_2\text{Se}<\text{H}_2\text{S}<\text{H}_2\text{O}\).
Step 4: Final Answer:
The correct order is C.