Full configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 5d¹ 6s²
In the short form, [Xe] stands for the 54 electrons of xenon, the noble gas before lanthanum. 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
Lanthanum puts its electron in 5d, not 4f. The 4f filling starts properly with cerium.
Configuration of lanthanum ions
| Ion | Configuration | Unpaired | Moment (BM) |
|---|---|---|---|
| La³⁺ | [Xe] | 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 |
|---|---|---|
| 54 | Xenon | [Kr] 4d¹⁰ 5s² 5p⁶ |
| 55 | Caesium | [Xe] 6s¹ |
| 56 | Barium | [Xe] 6s² |
| 58 | Cerium | [Xe] 4f¹ 5d¹ 6s² |
| 59 | Praseodymium | [Xe] 4f³ 6s² |
| 60 | Neodymium | [Xe] 4f⁴ 6s² |
Questions students ask
What is the electronic configuration of lanthanum?
[Xe] 5d¹ 6s², or in full, 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 5d¹ 6s². Lanthanum has atomic number 57.
How many electrons are in each shell of lanthanum?
2, 8, 18, 18, 9, 2 (K, L, M, N… shells in order).
How many unpaired electrons does lanthanum have?
1 in the ground state, so lanthanum atoms are paramagnetic.
What is the electronic configuration of La³⁺?
[Xe], with 0 unpaired electrons.
Why is lanthanum an exception?
Lanthanum puts its electron in 5d, not 4f. The 4f filling starts properly with cerium.