Question

(i) The acidic character of hydrides of group 15 increases from $H_{2}O$ to $H_{2}Te$. Why ?
(iI) Dioxygen is a gas while sulphur $\left(S_8\right)$ is a solid. Why?

Answer 1

1) Down the group, atomic size increases, and bond strength decreases. Hence, $H_{2}Te$ can release H-ion more easily than $H_{2}S$, making it more acidic. This trend in acidity is observed all along the periodic table. Size of central atom is directly proportional to the acidity of its hydride. Hence acidic character increases ongoing top to bottom in a group.

2)Oxygen occurs as $O_2$ molecule due to pπ-pπ bonding because of which the intermolecular forces in it are weak van der Waals forces as it is small in size with high electron density which tends to repel the other $O_2$ molecules. As a result, it exists as the gas.

On the other hand, sulphur does not form strong S=S double bonds hence exists as $S_8$ held together by strong covalent bonds and exists as a polyatomic molecule, in which intermolecular forces are strong so, it exists as a solid.