Question

The increasing order of volatility of hydrides of group 16 elements is:
A.${H_2}S{\text{ }} < {\text{ }}{H_2}O{\text{ }} < {\text{ }}{H_2}Se{\text{ }} < {H_2}Te$
B.${H_2}O{\text{ }} < {H_2}Te{\text{ }} < {\text{ }}{H_2}Se{\text{ }} < {\text{ }}{H_2}S$
C.${H_2}O{\text{ }} < {\text{ }}{H_2}S{\text{ }} < {\text{ }}{H_2}Se{\text{ }} < {H_2}Te$
D.None of these

Answer 1

The Volatility of a substance depends on different factors that include the molecular weight of the compound, presence of hydrogen bonding among the molecules, and the intermolecular forces of attraction.

Complete stepwise answer:
As we move down a group in the periodic table, the atomic weight of the element increases. Hence, the order of molecular weights of the hydrides of group 16 should be:${H_2}O{\text{ }} < {\text{ }}{H_2}S{\text{ }} < {\text{ }}{H_2}Se{\text{ }} < {H_2}Te$
Accordingly, as the molecular weight of ${H_2}Te$ is the highest, so it should be least volatile while ${H_2}O$ should have the highest volatility. But due to the high electronegativity difference between the hydrogen atom and the oxygen atom in the water molecules, there is intermolecular hydrogen bonding between the molecules which increases the intermolecular attraction and the volatility of ${H_2}O$ decrease below that of ${H_2}S.$
Hence the order of volatility of hydrides of group 16 elements is:
${H_2}S{\text{ }} < {\text{ }}{H_2}O{\text{ }} < {\text{ }}{H_2}Se{\text{ }} < {H_2}Te$

Hence, the correct option is option A.

Notes:
1.Hydrogen bonding is a type of molecular interaction that arises from the electronegativity differences between the molecules.
2.It is mainly seen in compounds having $F - H$ , $O - H$ and $N - H$ bonds, due to the high electronegativity of F, O, and N.
3.It is a mild dipole-dipole interaction whose strength is in the range of $4{\text{ kJ/mol}}$ to $50{\text{ kJ/mol}}$ of hydrogen bonds.
4.Due to the presence of hydrogen bonding, water is liquid in its natural state at room temperature while hydrogen sulphide is a gas.
5.The hydrogen bonds may be both intermolecular (between different molecules) as well as intramolecular (in the same molecule), for example in acetic acid.