Chemical Bonding Result Question 8
8. According to molecular orbital theory, which of the following will not be a viable molecule?
(2018 Main)
(a) $\mathrm{He}_2^{2+}$
(b) $\mathrm{He}_2^{+}$
(c) $\mathrm{H}^{-}_2$
(d) $\mathrm{H}_2^{2-}$
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Answer:
Correct Answer: 8. ( d )
Solution:
- Key Idea: According to M.O.T, the viability of any molecule can be judged through the calculation of bond order.
| Electronic | Configuration | Bond order |
|---|---|---|
| $\mathrm{He}_2^{+}$ | $\sigma_{1 s^2} \sigma_{1 s^1}^*$ | $\frac{2-1}{2}=0.5$ |
| $\mathrm{H}_2^{-}$ | $\sigma_{1 s^2} \sigma_{1 s^1}^*$ | $\frac{2-1}{2}=0.5$ |
| $\mathrm{H}_2^{2-}$ | $\sigma_{1 s^2} \sigma_{1 s^2}^*$ | $\frac{2-2}{2}=0$ |
| $\mathrm{He}_2^{2+}$ | $\sigma_{1 s^2}$ | $\frac{2-0}{2}=1$ |
The molecule having zero bond order will not be viable hence, $\mathrm{H}^{2-} _2$ (option d) is the correct answer.
BETA
