Full configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d⁵ 5s¹
In the short form, [Kr] stands for the 36 electrons of krypton, the noble gas before molybdenum. Only the electrons after it are written out.
Orbital diagram
Outer subshells only. Each box is an orbital; electrons fill singly first (Hund's rule), then pair up with opposite spins.
Why it's an exception
Molybdenum, like chromium above it, takes a half-filled 4d⁵ 5s¹ instead of 4d⁴ 5s².
Configuration of molybdenum ions
| Ion | Configuration | Unpaired | Moment (BM) |
|---|---|---|---|
| Mo⁶⁺ | [Kr] | 0 | 0.00 |
Moment is the spin-only magnetic moment μ = √(n(n + 2)) Bohr magnetons, where n is the number of unpaired electrons. Positive ions lose electrons from the outermost shell first, so transition metals lose their 4s or 5s electrons before d.
Nearby elements
| Z | Element | Configuration |
|---|---|---|
| 39 | Yttrium | [Kr] 4d¹ 5s² |
| 40 | Zirconium | [Kr] 4d² 5s² |
| 41 | Niobium | [Kr] 4d⁴ 5s¹ |
| 43 | Technetium | [Kr] 4d⁵ 5s² |
| 44 | Ruthenium | [Kr] 4d⁷ 5s¹ |
| 45 | Rhodium | [Kr] 4d⁸ 5s¹ |
Questions students ask
What is the electronic configuration of molybdenum?
[Kr] 4d⁵ 5s¹, or in full, 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d⁵ 5s¹. Molybdenum has atomic number 42.
How many electrons are in each shell of molybdenum?
2, 8, 18, 13, 1 (K, L, M, N… shells in order).
How many unpaired electrons does molybdenum have?
6 in the ground state, so molybdenum atoms are paramagnetic.
What is the electronic configuration of Mo⁶⁺?
[Kr], with 0 unpaired electrons.
Why is molybdenum an exception?
Molybdenum, like chromium above it, takes a half-filled 4d⁵ 5s¹ instead of 4d⁴ 5s².