Chemical Bonding Result Question 20
Objective Question
(One or more than one correct option)
20. According to molecular orbital theory, which of the following statements is(are) correct?
(2016 adv.)
(a) $\mathrm{C}_2^{2-}$ is expected to be diamagnetic
(b) $\mathrm{O}_2^{2+}$ is expected to have a longer bond length than $\mathrm{O}_2$
(c) $\mathrm{N}_2^{+}$ and $\mathrm{N}_2^{-}$ have the same bond order
(d) $\mathrm{He}_2^{+}$ has the same energy as two isolated He atoms
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Answer:
Correct Answer: 20. ( a,c )
Solution:
| Species | Electrons | MOEC | $N_B$ | $N_A$ | BO | Magnetic character |
|---|---|---|---|---|---|---|
| $\mathrm{C}_2^{2-}$ | 14 | $\sigma 1 s^2, \sigma * 1 s^2$ $\sigma 2 s^2, \sigma * 2 s^2$ $\pi 2 p_x^2 \approx-\pi 2 p_y^2$ $\sigma 2 p_z^2$ |
10 | 4 | 3 | Diamagnetic |
| $\mathrm{O}_2^{2+}$ | 14 | As above according to number of electrons | 10 | 4 | 3 | Diamagnetic |
| $\mathrm{O}_2$ | 16 | 10 | 6 | 2 | Paramagnetic | |
| $\mathrm{N}_2^{+}$ | 13 | 9 | 4 | 2.5 | Paramagnetic | |
| $\mathrm{N}_2^{-}$ | 15 | 10 | 5 | 2.5 | Paramagnetic | |
| $\mathrm{He}_2^{+}$ | 3 | 2 | 1 | 0.5 | Paramagnetic |
Thus, (a) is correct.
(b) Bond order $\mathrm{O}_2^{2+}>\mathrm{O}_2$ thus,
Bond length of $\mathrm{O}_2^{2+}<\mathrm{O}_2$ thus, incorrect.
(c) $\mathrm{N}_2^{+}$ and $\mathrm{N}_2^{-}$ have same bond order thus correct.
(d) $\mathrm{He}_2^{+}$ with bond order $=0.5$ is more stable thus, less energy than isolated He atoms. Thus, (d) is incorrect.
BETA
