Why does europium have 4f⁷ and not 4f⁶ 5d¹?

A half-filled 4f subshell (4f⁷, one electron per orbital) is exceptionally stable due to exchange-energy gains and symmetry. Europium promotes the "expected" 5d electron into 4f to reach this half-filled state, analogous to chromium and molybdenum in the d-block.

What are europium's common oxidation states?

Europium exhibits both +3 (the standard lanthanide state, losing 4f⁶ 6s²) and +2 (unusually stable because Eu²⁺ retains the half-filled [Xe] 4f⁷ core). The +3 state dominates in most compounds; the +2 state appears in EuO, EuS, and divalent salts.

How many valence electrons does europium have?

Europium has 9 valence electrons in the outermost shells: 7 in 4f and 2 in 6s. Chemically, it typically exposes 2–3 of these (the 6s pair plus one 4f electron) in bonding.

What block and period is europium in?

Europium is in Period 6 and belongs to the f-block (lanthanide series). It sits in Group 3 of the extended periodic table, between samarium (Z=62) and gadolinium (Z=64).

What is europium used for?

Europium is the primary red and blue phosphor activator in fluorescent lamps, CRT screens, and white LEDs. Eu³⁺ emits red light; Eu²⁺ emits blue. It is also used in euro banknote fluorescent security ink.

What is the noble-gas core for europium?

[Xe] represents the 54-electron xenon core: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶. The remaining 9 electrons (4f⁷ 6s²) are the valence region.

Europium Electron Configuration

Name: Europium Electron Configuration
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Author: Nham Vu

Quick reference for europium's ground-state electron configuration [Xe] 4f⁷ 6s², orbital diagram, quantum numbers, oxidation states, and key element facts.

Z = 63 Eu Europium

Europium — Electron Configuration

Atomic number 63 · Lanthanide (rare earth) · Period 6 · f-block

[Xe] 4f⁷ 6s² 63 electrons 9 valence e⁻ +2 / +3 states

Anomalous filling: Aufbau predicts [Xe] 4f⁶ 5d¹ 6s², but europium instead adopts [Xe] 4f⁷ 6s² because a half-filled 4f⁷ subshell (one electron per orbital) gains extra exchange energy, making it more stable than the predicted arrangement.

Subshell Breakdown (all 63 electrons)

Subshell	Type	Electrons	Max	Notation
1s	s, n=1	2	2	1s²
2s	s, n=2	2	2	2s²
2p	p, n=2	6	6	2p⁶
3s	s, n=3	2	2	3s²
3p	p, n=3	6	6	3p⁶
3d	d, n=3	10	10	3d¹⁰
4s	s, n=4	2	2	4s²
4p	p, n=4	6	6	4p⁶
4d	d, n=4	10	10	4d¹⁰
4f	f, n=4	7	14	4f⁷
5s	s, n=5	2	2	5s²
5p	p, n=5	6	6	5p⁶
6s	s, n=6	2	2	6s²
Total		63

Noble-Gas Shorthand

[Xe] 4f⁷ 6s²

[Xe] = 54-electron xenon core.

Full Configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f⁷ 5s² 5p⁶ 6s²

All 63 electrons written explicitly.

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 4f⁷ 25 / 32 electrons (78%)

Shell 5 (n=5) — 5s² 5p⁶ 8 / 50 electrons (16%)

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

Shell 4 holds 25 of its maximum 32 electrons. Shell 6 holds only the two 6s electrons — europium has no 6p, 5d, or 5f electrons.

Orbital Box Diagram — Valence Region

The [Xe] core (54 electrons in filled subshells) is collapsed for clarity. Only the 4f and 6s valence subshells are shown.

−3

−2

−1

7 electrons, one per orbital — half-filled 4f⁷ (all spin up, Hund's rule). No paired electrons in 4f.

2 electrons (paired, +½ and −½) — filled

Each box = one orbital. The mₗ values below the 4f boxes run from −3 to +3 (seven 4f orbitals). All seven carry one spin-up electron, giving europium a magnetic moment of 7 unpaired electrons.

Quantum Numbers — 4f and 6s Valence Electrons

Electron	n	l	mₗ	mₛ	Subshell
55 (6s)	6	0	0	+½	6s
56 (6s)	6	0	0	−½	6s
57 (4f)	4	3	-3	+½	4f
58 (4f)	4	3	-2	+½	4f
59 (4f)	4	3	-1	+½	4f
60 (4f)	4	3	0	+½	4f
61 (4f)	4	3	1	+½	4f
62 (4f)	4	3	2	+½	4f
63 (4f)	4	3	3	+½	4f

n = principal; l = azimuthal (l=3 → f); mₗ = magnetic (−l to +l); mₛ = spin. Electrons 1–54 occupy the [Xe] core (all subshells filled).

Common State (Eu³⁺)

Europium loses two 6s electrons and one 4f electron to form Eu³⁺.

Configuration: [Xe] 4f⁶

4f subshell is now partially filled with 6 electrons.

Standard lanthanide state, found in most compounds
Eu₂O₃, EuCl₃, Eu(NO₃)₃ are common Eu³⁺ compounds
Eu³⁺ is the red phosphor activator in fluorescent lamps

Unusual State (Eu²⁺)

Europium loses only its two 6s electrons to form Eu²⁺.

Configuration: [Xe] 4f⁷

Retains the stable half-filled 4f⁷ configuration — this is why Eu²⁺ is accessible.

Rare among lanthanides — most only show +3
EuO, EuS, EuSO₄ contain Eu²⁺
Eu²⁺ emits blue-green luminescence in phosphors

Ionization Summary

Ion	Electrons lost	Resulting config	Stability driver
Eu²⁺	2 (both 6s)	[Xe] 4f⁷	Half-filled 4f⁷ exchange energy
Eu³⁺	3 (6s² + one 4f)	[Xe] 4f⁶	Lanthanide contraction, +3 preferred in aqueous chemistry

Summary

Quick reference for europium's ground-state electron configuration [Xe] 4f⁷ 6s², orbital diagram, quantum numbers, oxidation states, and key element facts.

How it works

Europium's 63 electrons fill subshells following the Aufbau principle with one key exception.
The 4f subshell gains extra stability when exactly half-filled (7 electrons, one per orbital), so Eu promotes to [Xe] 4f⁷ 6s² instead of [Xe] 4f⁶ 5d¹ 6s².
Noble-gas shorthand replaces the inner xenon core ([Xe] = 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶) with [Xe] in brackets.
The resulting valence region is 4f⁷ 6s²: seven unpaired 4f electrons plus two paired 6s electrons.
Europium commonly forms +3 ions (losing 4f⁶ 6s² → [Xe] 4f⁶) and less commonly +2 ions (losing 6s² → [Xe] 4f⁷).
The half-filled 4f⁷ configuration of Eu²⁺ is especially stable, explaining europium's notable +2 chemistry among lanthanides.

Use cases

Chemistry homework and exam prep on lanthanide electron configurations.
Understanding why europium is anomalous compared to neighboring lanthanides.
Reference for +2 vs +3 oxidation state chemistry of rare-earth elements.
Teaching aid for 4f-block filling and Hund's rule in the f-block.
Comparing europium's configuration to gadolinium (half-filled 4f⁷ 5d¹) and samarium.
Materials science: europium is a red/blue phosphor dopant in LEDs and fluorescent lamps.
Verifying quantum numbers for 4f and 6s valence electrons.

Frequently Asked Questions

Last updated: 2026-07-23 · Reviewed by Nham Vu