What is the electron configuration of chlorine?

Chlorine's full electron configuration is 1s²2s²2p⁶3s²3p⁵. The condensed (noble-gas) shorthand is [Ne] 3s²3p⁵, where [Ne] represents the 10 electrons in the neon core.

How many valence electrons does chlorine have?

Chlorine has 7 valence electrons, all in the third shell (3s²3p⁵). That single vacancy in the 3p subshell drives its high electronegativity and reactivity.

Why is chlorine so reactive?

With 7 valence electrons, chlorine needs just one more to complete its octet and achieve the stable [Ar] configuration. This strong tendency to gain an electron makes Cl a powerful oxidizing agent and halogen.

What is the noble-gas shorthand for chlorine?

[Ne] 3s²3p⁵. Neon (element 10) has the same inner electron arrangement as the first 10 electrons of chlorine, so it abbreviates the core cleanly.

How many unpaired electrons does chlorine have?

Chlorine has one unpaired electron. The 3p subshell has three orbitals; two are fully paired and one holds a single spin-up electron, consistent with Hund's rule.

What charge does chlorine form as an ion?

Chlorine forms a Cl⁻ ion (chloride) by gaining one electron, giving it the electron configuration of argon: 1s²2s²2p⁶3s²3p⁶ (18 electrons total).

Chlorine Electron Configuration

Explore the complete electron configuration of chlorine (Cl, element 17) with interactive orbital diagrams, energy-level breakdown, and halogen chemistry context.

17 Cl 35.45

Chlorine

Halogen • Period 3 • Group 17

Atomic number: 17

Atomic mass 35.45 u

Valence electrons 7

Electronegativity 3.16 (Pauling)

Unpaired electrons 1

Display Mode

1s²2s²2p⁶3s²3p⁵

All 17 electrons listed explicitly across 5 subshells.

Compare with Neighbors

Sulfur (16) 1s²2s²2p⁶3s²3p⁴

Chlorine (17) 1s²2s²2p⁶3s²3p⁵

Argon (18) 1s²2s²2p⁶3s²3p⁶

Chlorine sits one electron below the full 3p⁶ of argon, driving its reactivity.

Energy Level Diagram

Filled orbital Half-filled (unpaired) Empty orbital

Chloride Ion (Cl⁻)

When chlorine gains one electron it becomes the chloride anion with 18 electrons — identical to argon's configuration:

1s²2s²2p⁶3s²3p⁶ [same as Ar]

The 3p subshell is now completely filled, giving Cl⁻ a stable octet and no unpaired electrons.

Why This Configuration Matters

High electronegativity (3.16) — the 7-electron outer shell creates strong nuclear pull on bonding pairs, making Cl the third most electronegative element after fluorine and oxygen.

Strong oxidizing agent — one vacancy in 3p means Cl readily accepts an electron from metals (NaCl, MgCl₂) and nonmetals alike.

Diatomic Cl₂ — the single unpaired 3p electron means two Cl atoms share one electron each to form a covalent single bond, satisfying both octets.

Aufbau & Hund's rule — electrons fill 1s → 2s → 2p → 3s → 3p in order of increasing energy; within 3p, one electron enters each orbital before any pairing begins.

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Summary

Chlorine (Cl) is element 17 with the electron configuration 1s²2s²2p⁶3s²3p⁵, placing 17 electrons across three energy levels. Its third shell holds 7 electrons — just one short of a full octet — which makes chlorine an exceptionally reactive halogen that readily gains one electron to achieve the stable argon configuration. This tool breaks down each subshell, shows the orbital box notation, and explains the chemical consequences of that lone vacancy in the 3p subshell.

How it works

Select a display mode — shorthand notation, full notation, or orbital box diagram.
The tool highlights the selected energy level so you can trace electron filling order.
Hover or tap any orbital box to see spin labels (spin-up ↑ and spin-down ↓) and subshell details.
Use the "Compare" panel to contrast chlorine with neighboring elements (S and Ar) side by side.
Read the chemistry notes below the diagram to understand reactivity and bonding behavior.

Use cases

Check electron configuration notation for chemistry homework or exams.
Understand why chlorine is a strong oxidizing agent and halogen.
Compare Cl to sulfur (S) and argon (Ar) to see periodic trends.
Learn Hund's rule and the Aufbau principle using a concrete example.
Prepare for AP Chemistry or university-level inorganic chemistry coursework.
Visualize orbital filling for the 3p subshell and unpaired electrons.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu