Question

Account for the following:
(i) $P{Cl}_5$ is more covalent than $P{Cl}_3$.
(ii) Iron on reaction with $HCl$ forms $Fe{Cl}_2$ and not $Fe{Cl}_3$.
(iii) The two $O-O$ bond lengths in the ozone molecule are equal.

Answer 1

(i) Greater the positive oxidation state of the central metal atom, greater is its polarising power and thus more is the covalent character of the bond formed between central metal atom and other atoms.

In $PC{l}_5$, the central metal atom, P is in +5 oxidation state, while in $PC{l}_3$ it in +3 oxidation state. Therefore, $PC{l}_5$ is more covalent than $PC{l}_3$

(ii) Iron rects with hydrochloric acid in the following manner, resulting in the release of dihydrogen gas.

$Fe+2HCl\to FeC{l}_2+H_2\uparrow$

The liberated dihydrogen gas may react with the available oxygen and gets converted to water molecule. This diminishes the chances of oxidation of ferrous chloride to ferric chloride. As a result $FeC{l}_3$ is not formed.

(iii) In ozone, the three oxygen atoms are arranged to form a bent shaped structure. The central oxygen atom makes a single bond with one of the terminal oxygen atoms and a double bond with the other terminal oxygen atom. But the $\pi$ electrons of double bond are delocalised over all the three oxygen atoms. Due to which the single and the double bond are not entirely pure but are the resonance hybrids of single and double bond respectively, giving rise to the O - O bond distance as the average bond distance of the single and double bond.