Question

The highest occupied molecular orbital for \(Ne_2\) is

• A. \(\sigma^{*}_{2p}\)
• B. \(\pi_{2p}\)
• C. \(\sigma_{2p}\)
• D. \(\pi^{*}_{2p}\)

Hint:

For molecules after nitrogen (O, F, Ne): Orbital order is \[ \sigma_{2p} \lt \pi_{2p} \lt \pi^{*}_{2p} \lt \sigma^{*}_{2p} \] For \(Ne_2\), the highest occupied orbital is always \[ \sigma^{*}_{2p} \] Memorize MO ordering carefully for chemistry exams.

Answer 1

The Correct Option is A

Concept: Molecular orbital theory explains formation of molecules by combination of atomic orbitals. Electrons occupy molecular orbitals according to Aufbau principle. Highest occupied molecular orbital (HOMO) means the highest energy orbital containing electrons.

Step 1: Find total electrons in \(Ne_2\).
Each neon atom contains \[ 10\; electrons \] Therefore molecule has \[ 20\; electrons \]

Step 2: Write molecular orbital filling order for oxygen family onwards.
For atomic number greater than 7, order is \[ \sigma_{1s} \] \[ \sigma^{*}_{1s} \] \[ \sigma_{2s} \] \[ \sigma^{*}_{2s} \] \[ \sigma_{2p} \] \[ \pi_{2p} \] \[ \pi^{*}_{2p} \] \[ \sigma^{*}_{2p} \]

Step 3: Fill 20 electrons.
Electronic arrangement becomes \[ (\sigma_{1s})^2 \] \[ (\sigma^{*}_{1s})^2 \] \[ (\sigma_{2s})^2 \] \[ (\sigma^{*}_{2s})^2 \] \[ (\sigma_{2p})^2 \] \[ (\pi_{2p})^4 \] \[ (\pi^{*}_{2p})^4 \] \[ (\sigma^{*}_{2p})^2 \]

Step 4: Identify HOMO.
Highest occupied orbital means orbital having greatest energy among occupied orbitals. Final occupied orbital is \[ \sigma^{*}_{2p} \] Therefore HOMO is \[ \boxed{\sigma^{*}_{2p}} \] \[ \boxed{\text{Correct Answer = Option (1)}} \]