Chemistry · Atomic structure

Electron Configuration and Orbital Diagram Explorer

Choose an element from hydrogen to krypton and an ion charge. The page fills the orbitals one electron at a time in the order of increasing energy, and shows the configuration, unpaired electrons, and effective nuclear charge.

Use the buttons to jump to chromium and copper, the two exceptions in this range, and to iron and its ions, where the 4s electrons leave before the 3d electrons.

Model notes

Filling order used: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p. Electrons enter boxes of the same subshell one at a time with parallel spins first (Hund's rule), then pair up. Each box holds at most two electrons with opposite spins (Pauli exclusion principle).
Chromium ([Ar] 4s¹ 3d⁵) and copper ([Ar] 4s¹ 3d¹⁰) are experimental exceptions: a half-filled or filled 3d subshell lowers the energy enough to move one 4s electron. Cations are made by removing electrons from the highest n first, so 4s electrons leave before 3d electrons.
Effective nuclear charge uses Slater's rules for the outermost electron. It is an estimate, not a measurement, and it is computed for the ion you choose.
Anions of transition metals are rare and are included only so the slider is continuous. The charge range is limited so that the electron count stays between 1 and 36.
Valence electrons are counted as the electrons in the outermost shell, plus the 3d electrons for the first-row transition metals Sc to Zn.

Sources

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