Question

(a) Account for the following:
(i) Acidic character increase from $HF$ to $HI$.
(ii) There is large difference between melting and boiling points of oxygen and sulphur.
(iii) Nitrogen does not from pentahalide.
(b) Draw the structures of the following:
(i) $Cl{F}_3$
(ii)$Xe{F}_4$

Answer 1

a.

(i) The acidic strength of the hydrohalic acids increase from $HF$ because the stability of the acids decrease from $HF$ to $HI$ on account of decrease in bond dissociation enthalpy of $H-X$ bond from $HF$ to $HI$.

(ii) The difference in melting point and boiling point of oxygen and sulphur is due to the difference in their atomicities, oxygen exists as a distance $\left(O_2\right)$ molecule, while sulphur exists as a polyatomic $\left(s_8\right)$ molecule and also oxygen is small in size and have high electro-negativity.

(iii) Being an element of second period, Nitrogen has no 'd' orbitals and its maximum covalency is restricted to four. Hence, due to the non-availability of d-orbitals, it can't form pentahalides.