Questions

# The increasing order of energies of various molecular orbitals are$\left(\mathrm{\pi }2{\mathrm{p}}_{\mathrm{x}}=\mathrm{\pi }2{\mathrm{p}}_{\mathrm{y}}\right)<\left({\mathrm{\pi }}^{*}2{\mathrm{p}}_{\mathrm{x}}={\mathrm{\pi }}^{*}2{\mathrm{p}}_{\mathrm{y}}\right)<{\sigma }^{*}2{\mathrm{p}}_{\mathrm{z}}$$<\mathrm{\sigma }2{\mathrm{p}}_{\mathrm{z}}<\left({\mathrm{\pi }}^{*}2{\mathrm{p}}_{\mathrm{x}}={\mathrm{\pi }}^{*}2{\mathrm{p}}_{\mathrm{y}}\right)<{\mathrm{\sigma }}^{*}2{\mathrm{p}}_{\mathrm{z}}$Choose the correct option.

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a
Order I is correct for all molecules and II is incorrect
b
Order II is correct for all molecules and I is incorrect
c
Order I is correct for O2 and F2 while order II is correct for B2,C2 and N2
d
Both order I and II are correct for all molecules

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detailed solution

Correct option is C

The increasing order of energies of various molecular orbitals for O2 and F2 (no. of e- >14) is given belowσ1s<σ*1s<σ2s<σ*2s<σ2pz<π2px=π2py<π*2px=π*2py<σ*2pzHowever, this sequence of energy levels of molecular orbitals is not correct for the remaining molecules Li2,Be2,   B2,  C2, N2. (no. of e- ≤14) For instance, it has been observed experimentally that for molecules such as B2,C2, N2 etc. the increasing order of energies of various molecular orbitals is σ1s<σ*1s<σ2s<σ*2s<(π2px=π2py<σ2pz <π*2px=π*2py<σ*2pzThe important characteristic feature of this order is that the energy of σ2pzmolecular orbital is higher than that of π2px and π2pymolecular orbitals.

Similar Questions

Consider the following statement.
I. When ${\mathrm{O}}_{2}$ is converted into ${\mathrm{O}}_{2}^{2+}$ bond order decreases.
II. ${\mathrm{O}}_{2}$ molecule is paramagnetic because it contains two unpaired electrons in ${\mathrm{\pi }}^{*}2{\mathrm{p}}_{\mathrm{x}}$ and ${\mathrm{\pi }}^{*}2{\mathrm{p}}_{\mathrm{y}}$ molecular orbitals.
III. The bond length in NO is greater than ${\mathrm{NO}}^{+}$.
Choose the correct option.