What is the electron configuration of fluorine?

Fluorine (F, Z=9) has the ground-state electron configuration 1s² 2s² 2p⁵. Its 9 electrons occupy three subshells across two shells.

What is the noble-gas shorthand for fluorine?

The condensed notation is [He] 2s² 2p⁵, where [He] represents the filled 1s² core shared with helium.

How many unpaired electrons does fluorine have?

Fluorine has one unpaired electron in the 2p subshell. The 2p⁵ configuration means two 2p orbitals are filled (paired) and one holds a single electron.

Why is fluorine the most electronegative element?

Fluorine has a high nuclear charge (Z=9) with only two inner-shell electrons shielding it, and its 2p subshell is one electron short of the stable neon configuration. This makes fluorine pull shared electrons toward itself more strongly than any other element.

How many valence electrons does fluorine have?

Fluorine has 7 valence electrons — 2 from the 2s subshell and 5 from the 2p subshell — all in the second shell (n=2).

What ion does fluorine typically form?

Fluorine gains one electron to reach the stable neon configuration (1s² 2s² 2p⁶), forming the fluoride ion F⁻ with a −1 charge.

What block of the periodic table is fluorine in?

Fluorine is in Period 2, Group 17 (the halogens), and belongs to the p-block because its last electron fills a p orbital (2p⁵).

Fluorine Electron Configuration

Name: Fluorine Electron Configuration
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Author: Nham Vu

Interactive reference for fluorine's electron configuration (1s² 2s² 2p⁵), orbital box diagram, quantum numbers, and key atomic properties.

Z = 9 F Fluorine

Fluorine — Electron Configuration

Atomic number 9 · Halogen · Period 2, Group 17 · p-block

1s² 2s² 2p⁵ [He] 2s² 2p⁵ 9 electrons 7 valence e⁻

Subshell Breakdown

Subshell	Type	Electrons	Max 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	5	6	2p⁵
Total		9

Full Configuration

1s² 2s² 2p⁵

All subshells written explicitly.

Noble-Gas Shorthand

[He] 2s² 2p⁵

[He] = 1s² (the filled helium core).

Shell Fill Summary

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

Shell 2 (n=2) — 2s² 2p⁵ 7 / 8 electrons (87.5%)

Shell 2 can hold up to 8 electrons (2s + 2p). Fluorine fills 7 of those 8 slots — just one short of the neon noble-gas configuration.

Why fluorine is so reactive

One electron away from neon's closed-shell configuration, fluorine has the highest electronegativity (3.98 Pauling scale) of any element. Its 2p⁵ configuration drives it to gain one electron and form F⁻ in nearly every chemical environment.

Orbital Box Diagram

2 electrons (paired) — filled

m=-1

m=0

m=+1

5 electrons — 2 pairs + 1 unpaired

Per Hund's rule, each 2p orbital receives one electron before any pairing. Fluorine's 2p⁵ fills two orbitals fully and leaves one with a single unpaired electron (highlighted in blue). Paired electrons have opposite spins (+½ and −½) per the Pauli exclusion principle.

Quantum Numbers for All 9 Electrons

e⁻ #	n	l	mₗ	mₛ	Subshell
1	1	0	0	+½	1s
2	1	0	0	−½	1s
3	2	0	0	+½	2s
4	2	0	0	−½	2s
5	2	1	−1	+½	2p
6	2	1	−1	−½	2p
7	2	1	0	+½	2p
8	2	1	0	−½	2p
9	2	1	+1	+½	2p (unpaired)

n = principal quantum number, l = azimuthal (0=s, 1=p), mₗ = magnetic, mₛ = spin. Electron 9 is fluorine's lone unpaired electron.

Summary

Interactive reference for fluorine's electron configuration (1s² 2s² 2p⁵), orbital box diagram, quantum numbers, and key atomic properties.

How it works

The Aufbau principle fills orbitals from lowest to highest energy: 1s, then 2s, then 2p.
Fluorine's 9 electrons fill 1s² (2 electrons), 2s² (2 electrons), and 2p⁵ (5 electrons).
The 2p subshell has three orbitals (ml = −1, 0, +1); Hund's rule fills each with one electron before pairing — two orbitals end up paired and one holds the single unpaired electron.
Noble-gas notation replaces the filled 1s² 2s² 2p⁶... wait — only [He] = 1s² applies here, giving [He] 2s² 2p⁵.
The orbital box diagram shows each electron as an arrow, with paired electrons in opposite directions per the Pauli exclusion principle.
The quantum numbers table lists all four quantum numbers (n, l, mₗ, mₛ) for each of the 9 electrons.

Use cases

Quick reference for chemistry homework or exam review.
Visualize Hund's rule and why fluorine has one unpaired electron.
Understand why fluorine is the most electronegative element (needs one more electron to reach neon's stable octet).
Compare fluorine to other halogens (chlorine, bromine) in terms of electron filling.
Learn noble-gas shorthand notation with a p-block element example.
Teaching aid for introductory atomic structure and periodic trends lessons.
Understand why fluorine readily forms the F⁻ ion by gaining one electron.

Frequently Asked Questions

Last updated: 2026-06-18 · Reviewed by Nham Vu