Orbital Filling Workbench

Drag electrons from the blue source into the highlighted lowest-energy subshell.

Aufbau: fill the lowest available energy level first — begin with 1s.

Aufbau Principle Lab

Build configurations using three connected rules.

Target atom

0placed

1target electrons

0outer shell

No electrons yet

Place the first electron in 1s, the lowest-energy orbital.

Next subshell1s

Rule being usedAufbau

Shell population0

Teacher / Demo mode

Aufbau chooses the subshell; Pauli limits each orbital; Hund chooses how equal-energy orbitals fill.

Electrons occupy available orbitals from lower energy to higher energy. The sequence shown is 1s, 2s, 2p, 3s, 3p, 4s, then 3d.

Each orbital box holds at most two electrons, and paired electrons have opposite spins.

Within p or d subshells, electrons occupy separate equal-energy orbitals with parallel spins before pairing.

The shell number is the first number in 2p or 3d. Subshell letters describe orbital type and capacity: s holds 2, p holds 6, d holds 10.

Score: 0 / 7