What is the noble-gas shorthand for lanthanum?

The condensed notation is [Xe] 5d¹ 6s², where [Xe] represents the filled 54-electron xenon core (1s² through 5p⁶).

Why does lanthanum have a 5d electron instead of 4f?

In lanthanum the 5d subshell is slightly lower in energy than the 4f subshell, so the first electron beyond the xenon core occupies 5d rather than 4f. Starting from cerium (Z=58) the 4f subshell begins filling.

How many valence electrons does lanthanum have?

Lanthanum has 3 valence electrons — one 5d¹ and two 6s². It loses all three to form the stable La³⁺ ion with the [Xe] noble-gas configuration.

What is lanthanum's most common oxidation state?

Lanthanum almost exclusively forms La³⁺ compounds (+3 oxidation state). Removing the three outer electrons (5d¹ 6s²) gives the stable xenon core, which makes +3 by far the most stable state.

What block and period is lanthanum in?

Lanthanum is in Period 6, Group 3, and is formally classified in the d-block (it fills a 5d electron) though it is the first member of the lanthanide (f-block) series. Its placement varies by convention between d-block and f-block groupings.

What are the quantum numbers for lanthanum's 5d valence electron?

The 5d¹ electron has n=5, l=2, mₗ=0 (or any of −2 to +2 by convention), mₛ=+½. The two 6s² electrons have n=6, l=0, mₗ=0, mₛ=+½ and −½.

Lanthanum Electron Configuration

Name: Lanthanum Electron Configuration
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Author: Nham Vu

Interactive reference for lanthanum's electron configuration ([Xe] 5d¹ 6s²), orbital box diagram, quantum numbers, and key chemical properties of the first lanthanide.

Z = 57 La Lanthanum

Lanthanum — Electron Configuration

Atomic number 57 · First lanthanide · Period 6, Group 3 · Rare-earth metal

[Xe] 5d¹ 6s² 57 electrons 3 valence e⁻ +3 oxidation state

Subshell Breakdown

Subshell	Type	Electrons	Max	Notation
1s	s orbital, shell n=1	2	2	1s²
2s	s orbital, shell n=2	2	2	2s²
2p	p orbitals, shell n=2	6	6	2p⁶
3s	s orbital, shell n=3	2	2	3s²
3p	p orbitals, shell n=3	6	6	3p⁶
4s	s orbital, shell n=4	2	2	4s²
3d	d orbitals, shell n=3	10	10	3d¹⁰
4p	p orbitals, shell n=4	6	6	4p⁶
5s	s orbital, shell n=5	2	2	5s²
4d	d orbitals, shell n=4	10	10	4d¹⁰
5p	p orbitals, shell n=5	6	6	5p⁶
5d	d orbitals, shell n=5	1	10	5d¹
6s	s orbital, shell n=6	2	2	6s²
Total		57

Full Configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 5d¹ 6s²

All 13 subshells written explicitly.

Noble-Gas Shorthand

[Xe] 5d¹ 6s²

[Xe] = the filled 54-electron xenon core.

Lanthanide Exception — Why 5d¹ instead of 4f¹?

In lanthanum the 5d subshell lies at slightly lower energy than the empty 4f subshell, so the first electron beyond the xenon core goes into 5d rather than 4f. Starting at cerium (Z=58), the 4f subshell drops below 5d in energy and begins filling — giving Ce the configuration [Xe] 4f¹ 5d¹ 6s². Lanthanum is therefore the d-block gateway to the f-block lanthanide series.

Shell Fill Summary

Shell 1 (n=1) — 1s² 2 / 2 electrons (100%)

Shell 2 (n=2) — 2s² 2p⁶ 8 / 8 electrons (100%)

Shell 3 (n=3) — 3s² 3p⁶ 3d¹⁰ 18 / 18 electrons (100%)

Shell 4 (n=4) — 4s² 4p⁶ 4d¹⁰ 18 / 32 electrons (56%)

Shell 5 (n=5) — 5s² 5p⁶ 5d¹ 9 / 50 electrons (18%)

Shell 6 (n=6) — 6s² 2 / 72 electrons (3%)

Shell 5 can hold up to 50 electrons (5s + 5p + 5d + 5f + 5g); lanthanum fills 5s², 5p⁶, and 5d¹ — 9 of 50. Shell 6 can hold up to 72; only 6s² used.

Orbital Box Diagram

[Xe] core: The inner 54 electrons (1s² through 5p⁶) form the xenon noble-gas core. All those orbitals are completely filled with paired electrons. Only the 5d and 6s subshells are shown individually below.

[Xe]

… 27 filled orbitals total

54 electrons — all paired, all filled

1 electron (unpaired, spin up) — one of 3 valence electrons

2 electrons (paired, spin up + spin down)

Each box represents one orbital. Up arrow = spin +½; down arrow = spin −½. Removing all three valence electrons (5d¹ 6s²) gives the stable La³⁺ ion with the [Xe] configuration.

Quantum Numbers — Valence Electrons

Electron #	n	l	mₗ	mₛ	Subshell	Note
54	5	1	1	−½	5p	last [Xe] core e⁻
55	5	2	0	+½	5d	valence — 5d¹ (lanthanide exception)
56	6	0	0	+½	6s	valence — 6s¹
57	6	0	0	−½	6s	valence — 6s² (paired)

n = principal; l = azimuthal (0=s, 1=p, 2=d); mₗ = magnetic; mₛ = spin. Electrons 1–54 fill the [Xe] core.

Summary

Interactive reference for lanthanum's electron configuration ([Xe] 5d¹ 6s²), orbital box diagram, quantum numbers, and key chemical properties of the first lanthanide.

How it works

The Aufbau principle fills orbitals from lowest to highest energy.
Lanthanum's 57 electrons fill the xenon core (1s through 5p) plus one 5d and two 6s electrons.
The noble-gas shorthand [Xe] 5d¹ 6s² replaces the 54-electron xenon core with [Xe] in brackets.
Unusually, the first lanthanide skips the 4f subshell — the lone 5d¹ electron sits slightly lower in energy.
The orbital diagram shows the 5d subshell with one unpaired electron and 6s with two paired electrons.
The element facts tab lists physical properties, ionization energies, and common uses of lanthanum.

Use cases

Quick-reference for chemistry homework or exam review on electron configurations.
Visualize how the Aufbau principle and lanthanide exception interact for element 57.
Understand why lanthanum has a +3 oxidation state (loses 5d¹ and 6s² electrons).
Compare lanthanum to neighboring elements barium (Z=56) and cerium (Z=58) in period 6.
Learn how the [Xe] 5d¹ 6s² configuration explains La³⁺ ion formation.
Teaching aid for atomic structure, periodic trends, and f-block chemistry.
Verify quantum numbers for lanthanum's valence electrons.

Frequently Asked Questions

Last updated: 2026-07-08 · Reviewed by Nham Vu