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What is the lowest energy unoccupied molecular orbital (LUMO) of  \mathrm{B_2 } molecule? 

Option: 1

\mathrm{\sigma 2 s}


Option: 2

\mathrm{ \sigma 2 p_z}


Option: 3

\mathrm{\sigma 2 p_x}


Option: 4

\mathrm{\Pi 2 \mathrm{p}_{\mathrm{y}}}


Answers (1)

\mathrm{B}_2 is a good example of the energy level shift cause by the mixing of s and p orbitals. In the absence of mixing the \sigma{2 \mathrm{Pz}} orbital is expected to be lower in energy than the { \pi{2 P x}} and \pi{2 P y} orbitals and the resulting molecule would be diamagnetic. However, mixing of orbitals lowers the energy of the \sigma{2 s} orbital and increases the energy of the \sigma{2 \mathrm{Pz}} orbitals to a higher level than the \pi{2 \mathrm{Px}} and \pi{2 \mathrm{Py}} orbitals, giving the order of energies shown in molecular orbital diagram. The lowest energy unoccupied molecular orbital (LUMOs) of \mathrm{B}_2 molecule is \sigma{2 \mathrm{Pz}}.

\mathrm{B}_2 is a good example of the energy level shift cause by the mixing of s and p orbitals. In the absence of mixing the \sigma{2 \mathrm{Pz}} orbital is expected to be lower in energy than the { \pi{2 P x}} and \pi{2 P y} orbitals and the resulting molecule would be diamagnetic. However, mixing of orbitals lowers the energy of the \sigma{2 s} orbital and increases the energy of the \sigma{2 \mathrm{Pz}} orbitals to a higher level than the \pi{2 \mathrm{Px}} and \pi{2 \mathrm{Py}} orbitals, giving the order of energies shown in molecular orbital diagram. The lowest energy unoccupied molecular orbital (LUMOs) of \mathrm{B}_2 molecule is \sigma{2 \mathrm{Pz}}.

Posted by

Sumit Saini

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