Chemical Bonding and Molecular Structure

Chemistry · Class 11

Simulation · Chemistry · Class 11

Fill a molecular orbital diagram

"Fill a molecular orbital diagram" is a free, interactive Class 11 Chemistry simulation for NEET and JEE, built on the NCERT section "Molecular orbital theory" in Chemical Bonding and Molecular Structure. Electrons fill an MO diagram for any second-period diatomic or ion by aufbau, Pauli and Hund; the σ2p/π2p order flips between N2-type and O2-type, with bond order, HOMO and magnetism readouts. NEET has asked about this idea 8 times in 10 years of papers. JEE Main asked 47 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).

From the lesson Homonuclear diatomic molecules in Chemical Bonding and Molecular Structure. Change the values and watch what happens.

Fill a molecular orbital diagramChemistry · Class 11

What it shows

NCERT § "Molecular Orbital Theory"

Electrons fill an MO diagram for any second-period diatomic or ion by aufbau, Pauli and Hund; the σ2p/π2p order flips between N2-type and O2-type, with bond order, HOMO and magnetism readouts.

Controls

3 to try

  • Segmentedmolecule H2 / He2 / Li2 / B2 / C2 / N2 / O2 / F2 / Ne2
  • Slidercharge −2 to +2
  • ToggleN2-type / O2-type ordering (auto, can override)

Try this

Find a species with bond order 2.5 that is paramagnetic (O2+ or N2−/N2+), and show that He2 has bond order 0.

Common mistake

O2 diamagnetic from its Lewis structure; using the N2 ordering for O2 (or O2 ordering for B2/C2).

In NEET

10 years of papers

Asked 8 times in 10 years of NEET.

See the past questions: Molecular Orbital Theory, Chemical Bonding and Molecular Structure (chapter)

In JEE Main

42 shifts analysed

47 questions from Chemical Bonding and Molecular Structure across the 42 JEE Main shifts Lumi has analysed (2017–2026).

See the past questions

The idea behind it

NCERT § "Bonding in Some Homonuclear Diatomic Molecules"

  • H₂: bond order 1, diamagnetic. He₂: bond order 0, so it is not stable.
  • Li₂: bond order 1, diamagnetic. B₂: bond order 1, paramagnetic because its two π2p electrons are unpaired.
  • C₂: bond order 2, diamagnetic, and both bonds are π bonds in the MO picture.
  • N₂: bond order 3, diamagnetic, with a very high bond enthalpy.
  • O₂: bond order 2 with two unpaired electrons in the π* orbitals, so it is paramagnetic, which the Lewis structure cannot explain.
  • Removing an antibonding electron raises bond order: O₂⁺ has 2.5; adding electrons lowers it: O₂⁻ has 1.5 and O₂²⁻ has 1.
  • F₂: bond order 1, diamagnetic. Ne₂: bond order 0, not formed.

Questions

5 answers

What does the "Fill a molecular orbital diagram" simulation show?
Electrons fill an MO diagram for any second-period diatomic or ion by aufbau, Pauli and Hund; the σ2p/π2p order flips between N2-type and O2-type, with bond order, HOMO and magnetism readouts.
What mistake does the "Fill a molecular orbital diagram" simulation fix?
A common mistake it clears up: O2 diamagnetic from its Lewis structure; using the N2 ordering for O2 (or O2 ordering for B2/C2).
Has NEET asked about this idea?
Yes. NEET has asked about this idea 8 times in 10 years of papers.
Does JEE Main ask questions from Chemical Bonding and Molecular Structure?
Yes. JEE Main asked 47 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
Is this simulation free?
Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "Homonuclear diatomic molecules" in Chemical Bonding and Molecular Structure (Class 11 Chemistry).

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