Keyboard: Tab selects the next electron domain, shown with a gold ring. Arrow keys nudge the selected domain about five degrees across the sphere; release and the shell relaxes. Left and right bracket keys rotate the view. Plus and minus change the number of domains between two and six. Press P to perturb the whole shell, R to reset. Watch the readouts settle to the canonical angle.

The Observatory · VSEPR

The Electron-Pair Orrery

RELAXING…

Field notes

Every electron domain — a bonding pair or a lone pair — is a cloud of negative charge, and like charges repel. Set free on the shell, the domains slide until they sit as far from one another as the sphere allows.

That single rule fixes the shape. Two go linear (180°), three trigonal planar (120°), four tetrahedral (109.5°), five trigonal bipyramidal, six octahedral (90°).

Nobody chooses these arrangements — repulsion dictates them. The 109.5° of the tetrahedron is not typed in here; it emerges as the shell relaxes, just as it does in a real methane molecule.

Gillespie & Nyholm named this VSEPR in 1957, distilling van’t Hoff’s 1874 tetrahedral carbon into one rule that predicts the shapes of thousands of molecules — a rule you can apply by hand.

Running light to keep it smooth.

Min angle—°

Spread—°

Repulsion—E

The Electron-Pair Orrery

This lab hit a snag