Molecular Orbital Builder: σ, σ*, π and π* Shapes in 3D
An interactive 3D builder for two-centre molecular orbitals. Pick any two of s, p, sp, sp² and sp³, overlap them head-on or side-on, and switch between bonding and antibonding to see the shape, the nodal planes, the cross-section and the energy-level diagram. Includes H₂, C–H, C–C, C=C, C≡C, C–Cl and C=O.
About this simulation
- What
- An interactive Chemistry simulation of Molecular Orbital Builder: σ, σ*, π and π* Shapes in 3D.
- Who
- Designed for AP, IB, and A‑Level Chemistry students.
- How
- Runs in any modern browser — drag, adjust, and explore in real time.
Updated 2026-10-11
Key Concepts
In phase and out of phase
Two overlapping orbitals combine two ways. Added in phase, they build up electron density between the nuclei: a bonding orbital. Added out of phase, they cancel there and leave a nodal plane between the nuclei: an antibonding orbital, marked with a star (σ*, π*).
σ and π
Head-on overlap along the bond axis gives σ orbitals, symmetric around the axis. Side-on overlap of parallel p orbitals gives π orbitals, with a nodal plane that contains the bond axis — electron density above and below the bond, none on it.
Antibonding rises more
Because the orbitals overlap, the antibonding level is pushed up further than the bonding level comes down. That is why He₂ (two electrons in σ, two in σ*) is not bound, and why the larger the overlap, the more lopsided the splitting.
Polar bonds tilt the orbitals
When one atom is more electronegative, its orbital lies lower. The bonding orbital then leans towards that atom and the antibonding orbital towards the other — which is why nucleophiles attack the carbon of C=O and the carbon of C–Cl.
What This Molecular Orbital Builder Shows
Most textbooks draw a σ bond as two lobes touching and σ* as the same lobes with a gap. The real shapes are more interesting: the bonding orbital merges into one region, the antibonding orbital has a sharp nodal plane, and a hybrid orbital keeps its small back lobe in both. This builder calculates each shape from the atomic orbitals instead of sketching it.
Choose any two of s, p, sp, sp² and sp³ and overlap them head-on (σ) or side-on (π). Switching between bonding and antibonding morphs one into the other, so you can watch the second orbital change sign. The cross-section below the 3D view shows the same orbital as a contour map, the slice most textbooks print, with the node drawn in.
The energy-level diagram and the electronegativity slider connect the shapes to chemistry: a polar bond's bonding orbital leans to the more electronegative atom and its antibonding orbital to the other. That is the orbital reason nucleophiles attack the carbon of a carbonyl group and the back of a C–Cl bond.
Frequently Asked Questions
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