Chemistry Q65 – NEET-UG 2023

Home Chemistry Chemical BondingQuestion #240

The correct order of energies of molecular orbitals of

N_{2}

molecule, is :

Clue 1 of 3: Molecular Orbital Theory

The energy order of molecular orbitals depends on the number of electrons in the diatomic molecule.

🥷

Ninja Strategy•Recall N

_{2}

MO Order

The key to solving this quickly is to remember the specific molecular orbital energy order for diatomic molecules with 14 or fewer electrons, where $π 2 p$ orbitals are lower in energy than $σ 2 p_{z}$ .

🧠 Full Solution Path

Step 1: Identify the Molecular Orbital Energy Order Rule✦ Active

For diatomic molecules with a total of 14 or fewer electrons (e.g., $N_{2}$ , $C_{2}$ , $B_{2}$ ), the energy order of molecular orbitals is:

σ 1 s < σ^{*} 1 s < σ 2 s < σ^{*} 2 s < (π 2 p_{x} = π 2 p_{y}) < σ 2 p_{z} < (π^{*} 2 p_{x} = π^{*} 2 p_{y}) < σ^{*} 2 p_{z}

For diatomic molecules with more than 14 electrons (e.g., $O_{2}$ , $F_{2}$ ), the energy order of molecular orbitals is:

σ 1 s < σ^{*} 1 s < σ 2 s < σ^{*} 2 s < σ 2 p_{z} < (π 2 p_{x} = π 2 p_{y}) < (π^{*} 2 p_{x} = π^{*} 2 p_{y}) < σ^{*} 2 p_{z}

Step 2: Determine Electron Count for N

_{2}

○ Expand

Nitrogen (N) has 7 electrons. Therefore, the $N_{2}$ molecule has $7 \times 2 = 14$ electrons.

Step 3: Apply the Correct Energy Order○ Expand

Since $N_{2}$ has 14 electrons, we use the energy order for molecules with 14 or fewer electrons. This order is $σ 1 s < σ^{*} 1 s < σ 2 s < σ^{*} 2 s < (π 2 p_{x} = π 2 p_{y}) < σ 2 p_{z} < (π^{*} 2 p_{x} = π^{*} 2 p_{y}) < σ^{*} 2 p_{z}$ . Comparing this with the given options, option (1) matches this order.

💡 Teacher's Secret Hint

Remember that the energy order of $σ 2 p_{z}$ and $π 2 p$ orbitals is inverted for molecules with 14 or fewer electrons due to s-p mixing.

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Chemistry Question 65 – NEET-UG 2023

Clue 1 of 3: Molecular Orbital Theory

🧠 Full Solution Path