What is the noble-gas shorthand for francium?

The condensed notation is [Rn] 7s¹, where [Rn] represents the filled 86-electron radon core (1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶).

How many valence electrons does francium have?

Francium has 1 valence electron — the single 7s¹ electron. It loses this electron to form the Fr⁺ ion with the [Rn] noble-gas configuration, the only common oxidation state.

Why is francium so rare?

Francium has no stable isotopes. The longest-lived isotope, Fr-223, has a half-life of only 22 minutes. It occurs naturally only as a short-lived decay product in uranium and thorium ore, and at any given moment less than 30 grams exist in the entire Earth's crust.

What block and period is francium in?

Francium is in Period 7, Group 1 (IA), and belongs to the s-block of the periodic table. It is the sixth and heaviest alkali metal below hydrogen, lithium, sodium, potassium, rubidium, and caesium.

What are the quantum numbers for francium's outermost electron?

The 7s¹ valence electron has n=7, l=0, mₗ=0, mₛ=+½.

How does francium's electron configuration compare to caesium?

Both have a single s¹ valence electron: caesium is [Xe] 6s¹ and francium is [Rn] 7s¹. Francium adds a full 4f (lanthanide) block and 5d block within its core compared to caesium, giving it 87 electrons vs. 55. Both form a +1 cation by losing their single valence electron.

Francium Electron Configuration

Name: Francium Electron Configuration
Availability: InStock
Author: Nham Vu

Interactive reference for francium's electron configuration ([Rn] 7s¹), orbital box diagram, quantum numbers, and key atomic properties of element 87.

Z = 87 Fr Francium

Francium — Electron Configuration

Atomic number 87 · Alkali metal · Period 7, Group 1 · s-block

[Rn] 7s¹ 87 electrons 1 valence e⁻ +1 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
6s	s orbital, shell n=6	2	2	6s²
4f	f orbitals, shell n=4	14	14	4f¹⁴
5d	d orbitals, shell n=5	10	10	5d¹⁰
6p	p orbitals, shell n=6	6	6	6p⁶
7s	s orbital, shell n=7	1	2	7s¹
Total		87

Full Configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s¹

All 16 subshells written explicitly (Aufbau order).

Noble-Gas Shorthand

[Rn] 7s¹

[Rn] = the filled 86-electron radon 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 18 / 50 electrons (36%)

Shell 6 (n=6) — 6s² 6p⁶ 8 / 72 electrons (11%)

Shell 7 (n=7) — 7s¹ 1 / 98 electrons (1%)

Shell 7 can hold up to 98 electrons (7s + 7p + 7d + 7f); francium uses only the first 7s¹ slot.

Orbital Box Diagram

[Rn] core: The inner 86 electrons (1s² through 6p⁶) form the radon noble-gas core. All those orbitals are completely filled with paired electrons. Only the 7s subshell is shown individually below.

[Rn]

… 43 filled orbitals total

86 electrons — all paired, all filled

1 electron (unpaired, spin up) — sole valence electron

Each box represents one orbital. An up arrow = spin +½ (spin-up). The single 7s¹ electron is unpaired. Removing it gives the stable [Rn] Fr⁺ ion.

Quantum Numbers — Valence Electron

Electron #	n	l	mₗ	mₛ	Subshell	Note
86	6	1	1	−½	6p	last [Rn] core e⁻
87	7	0	0	+½	7s	valence electron

n = principal; l = azimuthal (0=s, 1=p); mₗ = magnetic; mₛ = spin. Electrons 1–86 fill the [Rn] core.

Summary

Interactive reference for francium's electron configuration ([Rn] 7s¹), orbital box diagram, quantum numbers, and key atomic properties of element 87.

How it works

The Aufbau principle fills orbitals from lowest to highest energy.
Francium's 87 electrons fill the radon core (1s through 6p) plus one electron in 7s.
The noble-gas shorthand [Rn] 7s¹ replaces the 86-electron radon core with [Rn] in brackets.
The single 7s¹ electron is the lone valence electron responsible for Fr⁺ ion formation.
The orbital diagram shows the 7s subshell with one unpaired electron; all inner subshells are completely filled.
The element facts tab lists physical properties, ionization energy, and the extreme radioactivity of francium.

Use cases

Quick-reference for chemistry homework or exam review on electron configurations of heavy elements.
Visualize how the Aufbau principle fills s, p, d, and f subshells across seven shells.
Understand why francium is the most unstable naturally occurring element (all isotopes are radioactive).
Compare francium to lighter alkali metals (Li, Na, K, Rb, Cs) in group 1 periodic trends.
Learn how the 7s¹ configuration explains Fr⁺ ion formation and the +1 oxidation state.
Teaching aid for atomic structure, Period 7 elements, and group 1 chemistry.
Verify quantum numbers for francium's outermost electron.

Frequently Asked Questions

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