What is the electron configuration of americium?

Americium (Am, Z=95) has the ground-state configuration [Rn] 5f⁷ 7s², or in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ 5f⁷ 7s².

Why is the 5f⁷ configuration of americium stable?

A half-filled subshell (5f⁷ = 7 electrons in 7 orbitals, all with parallel spins) maximizes exchange energy — each pair of same-spin electrons lowers the total energy. This creates a particularly stable arrangement, analogous to Mn (3d⁵), Eu (4f⁷), and Gd (4f⁷ 5d¹ after promotion).

How many valence electrons does americium have?

Americium has 9 electrons outside the [Rn] core (5f⁷ 7s²). Its most common oxidation states are +3 (losing the two 7s electrons and one 5f electron) and +2 (losing only 7s electrons while retaining the half-filled 5f⁷).

What block is americium in?

Americium is an f-block element — its differentiating electrons enter the 5f subshell. It belongs to the actinide series, Period 7, and is the element directly below europium in the periodic table.

Is americium radioactive, and what is it used for?

Yes — all americium isotopes are radioactive. Am-241 (half-life 432.2 years) is the most commonly used isotope. It is the alpha-emitting source in household ionization-type smoke detectors, and Am-243 (half-life 7,370 years) is used in nuclear research.

Americium Electron Configuration

Name: Americium Electron Configuration
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Author: Nham Vu

Reference for americium's electron configuration: [Rn] 5f⁷ 7s² (full: 1s²…6p⁶ 5f⁷ 7s²). Includes orbital filling table, shell breakdown, and why the half-filled 5f⁷ is especially stable.

Z = 95 Am Americium

Americium — Electron Configuration

Atomic number 95 · Actinide series · Period 7 · f-block

[Rn] 5f⁷ 7s² 95 electrons 9 outer e⁻ Half-filled 5f⁷

Half-Filled 5f⁷ Stability

Americium's 5f subshell holds exactly 7 electrons — one in each of the seven 5f orbitals, all with parallel spins (Hund's rule). This half-filled arrangement maximizes exchange energy, lowering the total electronic energy. The effect is the same reason manganese prefers 3d⁵ and europium prefers 4f⁷. Because 5f⁷ is already especially stable, americium has a relatively low first ionization energy and prefers the +2 and +3 oxidation states rather than promoting electrons to 6d.

Noble-Gas Shorthand

[Rn] 5f⁷ 7s²

[Rn] = 86-electron radon core.

Full Expanded Configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ 5f⁷ 7s²

All 95 electrons written by subshell.

Subshell Breakdown

Subshell	Type	Electrons	Capacity	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
3d	d orbitals, shell n=3	10	10	3d¹⁰
4s	s orbital, shell n=4	2	2	4s²
4p	p orbitals, shell n=4	6	6	4p⁶
4d	d orbitals, shell n=4	10	10	4d¹⁰
4f	f orbitals, shell n=4	14	14	4f¹⁴
5s	s orbital, shell n=5	2	2	5s²
5p	p orbitals, shell n=5	6	6	5p⁶
5d	d orbitals, shell n=5	10	10	5d¹⁰
6s	s orbital, shell n=6	2	2	6s²
6p	p orbitals, shell n=6	6	6	6p⁶
5f	f orbitals, shell n=5	7	14	5f⁷
7s	s orbital, shell n=7	2	2	7s²
Total		95

Valence subshells (5f and 7s) are highlighted. All others form the [Rn] core.

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 4f¹⁴ 32 / 32 electrons (100%)

Shell 5 (n=5) — 5s² 5p⁶ 5d¹⁰ 5f⁷ 25 / 50 electrons (50%)

Shell 6 (n=6) — 6s² 6p⁶ 8 / 32 electrons (25%)

Shell 7 (n=7) — 7s² 2 / 32 electrons (6%)

Summary

Reference for americium's electron configuration: [Rn] 5f⁷ 7s² (full: 1s²…6p⁶ 5f⁷ 7s²). Includes orbital filling table, shell breakdown, and why the half-filled 5f⁷ is especially stable.

How it works

Americium's 95 electrons fill orbitals following the Aufbau principle, in order of increasing energy.
Radon ([Rn], Z=86) provides the filled core: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶.
After the [Rn] core, the 5f sublevel fills before 6d because 5f lies lower in energy at Z=95.
Seven electrons enter 5f — one per orbital (Hund's rule), creating a half-filled 5f⁷ arrangement with all spins parallel.
The two remaining electrons occupy 7s², giving the ground-state configuration [Rn] 5f⁷ 7s².
The half-filled 5f⁷ is exceptionally stable due to symmetric exchange energy, similar to Eu (Z=63) in the lanthanide row.

Use cases

Chemistry reference for students studying actinide or transuranium element configurations.
Understand why the half-filled 5f⁷ subshell is energetically favorable.
Compare americium's configuration with europium ([Xe] 4f⁷ 6s²) in the lanthanide series.
Verify quantum numbers and subshell counts for exam preparation.
Teaching aid for periodic trends, electron shielding, and Hund's rule in f-block elements.
Reference for nuclear chemistry and actinide series properties.

Frequently Asked Questions

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