Explain why ${\mathrm{PCl}}_5$ is trigonal bipyramidal whereas ${\mathrm{IF}}_5$ is square pyramidal.

Write Lewis structure of the following compounds and show formal charge on each atom.

${\mathrm{HNO}}_3, {\mathrm{NO}}_2, {\mathrm{H}}_2{\mathrm{SO}}_4$

The energy of $\mathrm{\sigma }2{\mathrm{p}}_{\mathrm{z}}$ molecular orbital is greater than $\mathrm{\pi }2{\mathrm{p}}_{\mathrm{x}}$ and $\mathrm{\pi }2{\mathrm{p}}_{\mathrm{y}}$ molecular orbitals in nitrogen molecule. Write the complete sequence of energy levels in the increasing order of energy in the molecule. Compare the relative stability and the magnetic behaviour of the following species :

${\mathrm{N}}_2, {\mathrm{N}}_2^{+} , {\mathrm{N}}_2^{-} , {\mathrm{N}}_2^{2+}$

What is the effect of the following processes on the bond order in ${\mathrm{N}}_2$ and ${\mathrm{O}}_2$?

(i)${\mathrm{N}}_2\to {\mathrm{N}}_2^{+} + {\mathrm{e}}^{–}$                                  (ii) ${\mathrm{O}}_2 \to {{\mathrm{O}}_2}^{+} +{\mathrm{e}}^{-}$

Give reason for the following :

Covalent bonds are directional bonds while ionic bonds are non-directional.

Give reason for the following :

Water molecule has bent structure whereas carbon dioxide molecule is linear.

Give reason for the following :

Ethyne molecule is linear.