---
title: "Chlorine (Cl): Atomic Mass, Electron Configuration & Properties"
url: https://www.moldraw.com/elements/chlorine.html
description: "Chlorine (Cl), element 17: atomic mass 35.45, electron configuration [Ne] 3s² 3p⁵, group 17, period 3, p-block reactive nonmetal. Melting and boiling point, density, electronegativity and shells."
lang: en
publisher: Scidart Academy
generated: 2026-11-03
---
17Cl35.45

# Chlorine (Cl) – element 17

Chlorine is a chemical element with the symbol **Cl** and atomic number **17**. It is a reactive nonmetal in group 17 (halogens), period 3 of the periodic table (p-block), and is a gas at room temperature.

Chlorine (Cl) has atomic number 17, atomic mass 35.45 u and electron configuration [Ne] 3s2 3p5.

[Download periodic table PDF](https://www.moldraw.com/printables/periodic-table.pdf)[Open interactive periodic table](https://www.moldraw.com/tools/free-chem-tools/interactive-periodic-table.html)

## Chlorine facts

| Symbol | Cl |
| --- | --- |
| Atomic number | 17 |
| Atomic mass | 35.45 u (g/mol) |
| Category | reactive nonmetal |
| Group | group 17 (halogens) |
| Period | 3 |
| Block | p-block |
| Phase at 20 °C | Gas |
| Electron configuration | 1s2 2s2 2p6 3s2 3p5 |
| Noble-gas notation | [Ne] 3s2 3p5 |
| Electrons per shell | 2, 8, 7 |
| Valence electrons | 7 |

## Bohr model and shells

Chlorine has 17 electrons in 3 shells: 2, 8, 7. Full configuration and noble-gas notation are in the table; work out any element or ion with the [electron configuration calculator](https://www.moldraw.com/tools/free-chem-tools/electron-configuration-calculator.html).

## Physical and atomic properties

| Melting point | 171.6 K (-101.5 °C) |
| --- | --- |
| Boiling point | 239.11 K (-34.0 °C) |
| Density | 3.2 g/L |
| Electronegativity (Pauling) | 3.16 |
| Electron affinity | 348.575 kJ/mol |
| Ionization energies | 1251.2, 2298, 3822 kJ/mol (1st, 2nd, 3rd) |
| Discovered by | Carl Wilhelm Scheele |

Use the atomic mass in the [molar mass calculator](https://www.moldraw.com/tools/free-chem-tools/molar-mass-calculator.html) for any formula containing Cl.

## Position in the periodic table

Tap any element to open its page.

## Molecules with chlorine

- [Chloroform](https://www.moldraw.com/molecules/chloroform.html)
- [Hydrogen chloride](https://www.moldraw.com/molecules/hydrogen-chloride.html)

Rotate each one in 3D, or draw your own structure in [MolDraw](https://www.moldraw.com/).

## Frequently asked questions

### What is the atomic mass of chlorine?

The atomic mass of chlorine is 35.45 u, so one mole of chlorine atoms weighs 35.45 g.

### What is the electron configuration of chlorine?

Chlorine has 17 electrons: 1s² 2s² 2p⁶ 3s² 3p⁵, or [Ne] 3s² 3p⁵ in noble-gas notation. Electrons per shell: 2, 8, 7.

### How many valence electrons does chlorine have?

Chlorine has 7 valence electrons (group 17).

### Is chlorine a metal?

No. Chlorine is a nonmetal (reactive nonmetal).

### Where is chlorine on the periodic table?

Chlorine is in group 17 (halogens), period 3, in the p-block.

Data: [Periodic-Table-JSON](https://github.com/Bowserinator/Periodic-Table-JSON) (CC BY-SA 3.0); standard atomic weights from IUPAC (abridged). Values in brackets are the mass number of the longest-lived isotope.