Electronic configuration of molybdenum

Electrons in each shell

Molybdenum has 42 electrons arranged as 2, 8, 18, 13, 1 across 5 shells, which is why it sits in period 5.

How to write it

Start from the previous noble gas core, written in square brackets, then add the remaining electrons in filling order. For molybdenum that gives [Kr] 4d⁵ 5s¹.

Exception to the Aufbau rule. Filling orbitals in order would give 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d⁴, but the real configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d⁵ 5s¹ because half-filled 4d⁵ is extra stable, just like chromium above it.

Molybdenum at a glance

Other elements in group 6