Undergraduate · 15 min

Mixing s and p orbitals: sp, sp² and sp³ hybrids

Morph the hybridisation type and watch how one s orbital plus p orbitals reorganise into equivalent lobes pointing along a line, a triangle or a tetrahedron.

Goal

Match each hybridisation (sp, sp², sp³) to a molecular geometry and to a carbon compound: ethyne, ethene, methane.

Apparatus and reagents

One s orbital and up to three p orbitals of a carbon atom; toggling “atoms” caps each hybrid lobe with a bonded neighbour.

Procedure

Start at sp³ and count the four lobes; rotate until you recognise the tetrahedron of $\ce{CH4}$ .
Switch to sp²: the three lobes flatten into a plane at 120°, like the bonds in $\ce{C2H4}$ ; imagine the leftover p orbital perpendicular to that plane.
Switch to sp: two lobes point in opposite directions, the geometry of $\ce{C2H2}$ or $\ce{CO2}$ .
Toggle the neighbouring atoms on and off and check each lobe axis matches a bond direction.

What to observe

sp gives a 180° line, sp² a flat 120° trigonal arrangement, sp³ a 109.5° tetrahedron — the hybrids always point as far apart as possible.
Each hybrid keeps a small opposite lobe; the big lobe concentrates electron density where the bond forms.
The number of hybrid orbitals always equals the number of atomic orbitals mixed: 1s + 1p → 2, 1s + 2p → 3, 1s + 3p → 4.

Explanation

Hybridisation recombines the atom’s orbitals into new equivalent orbitals that maximise overlap along bond directions. Mixing one s with $k$ p orbitals yields $k+1$ hybrids whose ideal geometries follow from symmetry: linear sp, trigonal-planar sp², tetrahedral sp³. The unhybridised p orbitals that remain (two for sp, one for sp²) form the π bonds of double and triple bonds — a first step from single-electron orbitals toward molecular-orbital and Hartree–Fock descriptions of bonding.

Chemists behind it

Linus Pauling