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

the acidic character depends on the ability of a compound to give up a hydrogen ion. Therefore, for this to happen the bond strength should be weak. Dioxygen is a compound containing two oxygen atoms which can only form diatomic compound whereas sulphur forms polyatomic compounds

Complete step by step answer:
i.The acidic character can be defined as the property of a compound to become an anion upon releasing a proton.
This character increases from left to right across the periodic table. This occurs due to many reasons. Namely, increase in the oxidation state. The more the oxidation state of an element more is its acidic property.
In this case mentioned in the question, the acidic character of hydrides increases down the group. This can be explained by the bond length of the compound. If the bond length between the element and hydrogen is long, it means that the bond is not strong.
Therefore, the bond can be broken easily. As we go down the group we can see that the bond length increases. Therefore, the compound can give up a hydrogen ion. In addition to this, there is hydrogen bond in water which makes it harder to release a hydrogen ion.
And hence we can say that acidic character of hydrides of group 15 increases from ${H_2}O\;$ to ${H_2}Te$.
ii.Dioxygen is a gas that consists of two oxygen atoms attached to each other with a double bond. Oxygen contains only $s$ and $p$ orbitals. It does not have a $d$ orbital. Therefore, it can only have a maximum oxidation state of $- 2$ . whereas sulphur contains $d$ orbitals and can accommodate more electrons which will occupy the $d$ orbital. Hence sulphur can form polyatomic compounds whereas oxygen can only form a diatomic compound.

Note: The acidic character increases with increase in bond length.
Therefore, the order of acidity is: ${H_2}O < {H_2}S < {H_2}Se < {H_2}Te$
As sulphur has $d$ orbitals it can accept many more electrons from other atoms. Thus it can form ${S_8}$ compound.