NEETChemistryChemical Bonding and Molecular Structure
Which of the following diatomic molecules has a bond order of 2 consisting entirely of bonds, and what is the correct molecular orbital energy justification for this?
Options
- AC ₂ , because the energy of the _ 2p_x and _ 2p_y orbitals is lower than that of the _ 2p_z orbital.
- BC ₂ , because the energy of the _ 2p_z orbital is lower than that of the _ 2p_x and _ 2p_y orbitals.
- CO ₂ , because the presence of electrons in the ^ * _ 2p_x and ^ * _ 2p_y orbitals cancels the bond.
- DN ₂ , because it has a triple bond and the _ 2p_z orbital is highest in energy among the bonding orbitals.
Correct answer
A. C ₂ , because the energy of the _ 2p_x and _ 2p_y orbitals is lower than that of the _ 2p_z orbital.
Step-by-step solution
The electronic configuration of the C ₂ molecule (12 electrons) is _ 1s ^2 , ^ * _ 1s ^2 , _ 2s ^2 , ^ * _ 2s ^2 , _ 2p_x ^2 = _ 2p_y ^2 . For molecules with 14 or fewer electrons (like C ₂ ), 2 s -2 p mixing causes the _ 2p_z orbital to be higher in energy than the _ 2p_x and _ 2p_y orbitals. Because the last four valence electrons fill the degenerate orbitals while leaving the _ 2p_z orbital empty, the bond order is 8-4 2 = 2 , and both bonds are bonds. If _ 2p_z were lower in energy, the molecule would have one