Made Easy Chemistry

Electron Configuration Anomalies

Some of the elements have electron configurations that differ slightly from what our general procedure would lead us to predict. Because a few of these elements are important elements, it is useful to know their actual electron configurations. Six of these are listed on the table below.

Unusual Electron Configurations

Element

Predicted Electron Configuration

Actual Electron Configuration

copper, Cu

[Ar] 3d⁹ 4s²

[Ar] 3d¹⁰4s¹

silver, Ag

[Kr] 4d⁹ 5s²

[Kr] 4d¹⁰ 5s¹

gold, Au

[Xe] 4f¹⁴ 5d⁹ 6s²

[Xe] 4f¹⁴ 5d¹⁰ 6s¹

palladium, Pd

[Kr] 4d⁸ 5s²

[Kr] 4d¹⁰

chromium, Cr

[Ar] 3d⁴ 4s²

[Ar] 3d⁵ 4s¹

molybdenum, Mo

[Kr] 4d⁴ 5s²

[Kr] 4d⁵ 5s¹

Element	Predicted Electron Configuration	Actual Electron Configuration
copper, Cu	[Ar] 3d⁹ 4s²	[Ar] 3d¹⁰4s¹
silver, Ag	[Kr] 4d⁹ 5s²	[Kr] 4d¹⁰ 5s¹
gold, Au	[Xe] 4f¹⁴ 5d⁹ 6s²	[Xe] 4f¹⁴ 5d¹⁰ 6s¹
palladium, Pd	[Kr] 4d⁸ 5s²	[Kr] 4d¹⁰
chromium, Cr	[Ar] 3d⁴ 4s²	[Ar] 3d⁵ 4s¹
molybdenum, Mo	[Kr] 4d⁴ 5s²	[Kr] 4d⁵ 5s¹