InterviewSolution
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InterviewSolution
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Which of the following is the correct order of stability?A. `H_2gtH_2^(+)gtHe_2gtHe_2^(+)`B. `H_2gtHe_2^(+)gtH_2^(+)gtHe_2`C. `H_2gtH_2^(+)gtHe_2^(+)gtHe_2`D. `H_2gtHe_2gtH_2^(+)gtHe_2^(+)` |
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Answer» Correct Answer - C Stability of a molecule is directly related to the value of bond order. Thus, the higher the bond order, the greater the stability. If two species have the same bond order `(bo)`, then the stability should be decided by the number of antibonding electrons. The lesser the number of antibonding electrons, the greater the stability. `H_2^(+)` is `(sigma_(1s))^1`. Thus, `bo=(N_b-N_a)/(2)=(1-0)/(2)=0.5` `H_2` is `(sigma_(1s))^2`. Thus, `bo=(2-0)/(2)=1` `He_2^(+)` is `(sigma_(1s))^2(sigma_(1s)^**)^1`. Thus, `bo=(2-1)/(2)=0.5` `He_2` is `(sigma_(1s))^2(sigma_(1s)^**)^2`. Thus, `bo=(2-2)/(2)=0` Both `H_2^(+)` and `H_2^(+)` have equal bond orders but `H_2^(+)` has zero antibonding electrons while `He_2^(+)` has one antibonding electron. Thus, `H_2^(+)` is relatively more stable. The correct order of stability is, thus, `H_2gtH_2^(+)gtHe_2^(+)gtHe_2` Moreover, `H_2^(+)` is somewhat more stable than `He_2^(+)` since there is only one electron in the hydrogen molecule ion and, therefore, it has no electron-electron repulsion. Furthermore, `H_2^(+)` also has less nuclear repulsion than `He_2^(+)`. |
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