Q1 / 180 · KCET 2009 · Chemistry

The correct statement with regard to $\mathrm{H}_{2}^{+}$and $\mathrm{H}_{2}^{-}$ is

  • A
    both $\mathrm{H}_{2}^{+}$and $\mathrm{H}_{2}^{-}$are equally stable
  • B
    both $\mathrm{H}_{2}^{+}$and $\mathrm{H}_{2}^{-}$do not exist
  • C
    $\mathrm{H}_{2}^{-}$is more stable than $\mathrm{H}_{2}^{+}$
  • Correct answer
    D
    $\mathrm{H}_{2}^{+}$is more stable than $\mathrm{H}_{2}^{-}$

Solution

$\mathrm{H}_{2}^{+}: \sigma 1 \mathrm{~s}^{1}, \stackrel{*}{\sigma} 1 \mathrm{~s}^{0}$ Bond order $=\frac{1}{2}$ $\mathrm{H}_{2}^{-}: \sigma 1 \mathrm{~s}^{2}, \stackrel{*}{\sigma} 1 \mathrm{~s}^{1}$ Bond order $=\frac{2-1}{2}=\frac{1}{2}$ The bond order of $\mathrm{H}_{2}^{+}$and $\mathrm{H}_{2}^{-}$are same but $\mathrm{H}_{2}^{+}$is more stable than $\mathrm{H}_{2}^{-}$. It is due to the presence of one electron in the antibonding molecular orbital in $\mathrm{H}_{2}^{-}$.

Hence, the correct answer is option: 'D'.

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