Molecular Orbital Diagram of N2 (MO Configuration, Bond Order, Magnetism)
Chemistry · Chemical Bonding · NEET
Nitrogen (N2) has 14 electrons. When you fill them into molecular orbitals, the special rule for N2 is that the two pi 2p orbitals sit BELOW the sigma 2p_z orbital. This gives a bond order of 3 (a triple bond) and leaves zero unpaired electrons, so N2 is diamagnetic. Memory hook: "N2 = 14 electrons, pi before sigma, bond order 3, all paired."
N2 MO diagram: 14 electrons fill up to sigma 2p_z, with the pi 2p orbitals lying BELOW sigma 2p_z (s-p mixing). All electrons are paired, giving bond order 3 and a diamagnetic molecule.
Your doubts, answered
How many electrons do I fill in the N2 MO diagram?
Each nitrogen atom has 7 electrons, so N2 has 7 + 7 = 14 electrons total. You fill all 14 into molecular orbitals from lowest energy to highest, following Aufbau, Pauli and Hund rules, exactly like atomic orbitals.
Why is pi 2p BELOW sigma 2p in N2 (and not above)?
For light molecules with 14 or fewer electrons (up to N2), the 2s and 2p orbitals are close in energy, so they mix (s-p mixing). This mixing pushes the sigma 2p_z orbital UP, so it ends up above the two pi 2p orbitals. The order becomes ...pi 2p_x = pi 2p_y < sigma 2p_z. For O2 and F2 (more than 14 electrons) this mixing is weak, so sigma 2p_z drops back below the pi orbitals. NEET loves testing this exact difference.
What is the full molecular orbital configuration of N2?
N2: sigma 1s^2, sigma* 1s^2, sigma 2s^2, sigma* 2s^2, (pi 2p_x^2 = pi 2p_y^2), sigma 2p_z^2. The inner 1s pair is often written as KK. So the short form is KK (sigma 2s)^2 (sigma* 2s)^2 (pi 2p_x^2 = pi 2p_y^2) (sigma 2p_z)^2.
How do I calculate the bond order of N2?
Bond order = 1/2 (Nb - Na), where Nb = bonding electrons and Na = antibonding electrons. In N2, Nb = 10 (sigma 2s + pi 2p_x + pi 2p_y + sigma 2p_z, plus sigma 1s) and Na = 4. Bond order = 1/2 (10 - 4) = 3. This matches the N triple bond (one sigma + two pi).
Is N2 paramagnetic or diamagnetic?
N2 is diamagnetic. Every molecular orbital in N2 is completely filled with paired electrons, so there are ZERO unpaired electrons. A molecule is paramagnetic only if it has one or more unpaired electrons. This is the opposite of O2, which has 2 unpaired electrons and IS paramagnetic.
Why is N2 so stable and unreactive?
Its bond order is 3, the highest common bond order. A triple bond is very strong (bond enthalpy about 946 kJ/mol) and short, so a lot of energy is needed to break N2 apart. That is why nitrogen gas is chemically inert at room temperature.
⚠️ The NEET trap ✗ Using the O2/F2 energy order for N2, i.e. placing sigma 2p_z BELOW the pi 2p orbitals. ✓ For N2 (14 electrons or fewer, i.e. B2, C2, N2), s-p mixing raises sigma 2p_z ABOVE the pi 2p orbitals: order is ...sigma* 2s < (pi 2p_x = pi 2p_y) < sigma 2p_z < (pi* 2p_x = pi* 2p_y) < sigma* 2p_z. 🧠 Remember the cut-off at N2: 'Up to N2, pi comes first; from O2, sigma comes first.'
Real NEET questions
NEET 2023 Phase 1
The correct order of energies of the molecular orbitals of the N2 molecule is:
Solution: For molecules with 14 or fewer electrons (like N2), s-p mixing raises the sigma 2p_z orbital, so the pi 2p_x and pi 2p_y orbitals lie BELOW sigma 2p_z. This gives the order in option A: ...sigma* 2s < (pi 2p_x = pi 2p_y) < sigma 2p_z < (pi* 2p_x = pi* 2p_y) < sigma* 2p_z.
NEET 2019 Odisha
Which of the following is paramagnetic?
A · N2
B · H2
C · Li2
D · O2 ✓
Solution: By MO theory, O2 has two unpaired electrons in its degenerate pi* 2p antibonding orbitals, so it is paramagnetic. N2, H2 and Li2 have all electrons paired, so they are diamagnetic. This confirms that N2 is NOT paramagnetic.
NEET 2017
Which one of the following pairs of species have the same bond order?
A · CO, NO
B · O2^-, NO^+
C · CN^-, CO ✓
D · N2, O2^-
Solution: Bond order 3 for both CN^- (14 e-) and CO (14 e-), which are isoelectronic with N2. NO has 2.5, O2^- has 1.5. N2 has bond order 3, but O2^- has 1.5, so the N2/O2^- pair does not match. Only CN^-/CO share the same bond order.
Solved Chemical Bonding NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
3. Bond order = 1/2 (10 bonding - 4 antibonding) = 3, which is a triple bond (one sigma + two pi bonds).
How many unpaired electrons are in N2?
Zero. All 14 electrons are paired, so N2 is diamagnetic.
Does N2 have pi 2p below or above sigma 2p?
Below. Because N2 has 14 electrons, s-p mixing raises sigma 2p_z above the pi 2p orbitals, so pi 2p is filled before sigma 2p_z.
What happens to the MO order for O2 and F2?
For O2 and F2 (more than 14 electrons), s-p mixing is weak, so sigma 2p_z drops below the pi 2p orbitals. This is the reverse of the N2 order and is a common NEET trap.
Why is N2 stronger than O2?
N2 has bond order 3 (triple bond) while O2 has bond order 2 (double bond). A higher bond order means a shorter, stronger bond, so N2 has a higher bond enthalpy and is harder to break.
