Question

Giving suitable reasons, arrange the hydrides of group 16 elements in the decreasing order of their thermal stability.

Answer 1

1. The decreasing order of hydrides of group 16 elements according to their thermal stability is H₂O > H₂S > H₂Se > H₂Te.
2. The size of the central atom increases down the group, resulting in weaker \[\ce{M - H}\] bonds.
3. Weaker \[\ce{M - H}\] bonds make hydrides less thermally stable as we move from H₂O to H₂Te.
4. Water is extra stable due to strong hydrogen bonding among molecules.
5. For example, water dissociates at about 2073-2273 K, whereas H₂S dissociates around 873 K. Thus, thermal stability decreases down the group because of increasing atomic size and decreasing bond strength, with water being the most stable because of hydrogen bonding.