017Reactive nonmetal · Group 17 · Period 3
Chlorine
Chlorine (Cl) is element 17, a reactive nonmetal in the p-block — group 17, period 3. It is a gas at room temperature with 3 electron shells (2, 8, 7) and an atomic mass of 35.45 u.
- Atomic mass
- 35.45 u
- Phase · STP
- gas
- Melting
- 172 K · -102 °C
- Boiling
- 239 K · -34 °C
- Electronegativity
- 3.16
- Density
- 3.2 g/cm³
Photograph — Benjah-bmm27, Public domain, via Wikimedia Commons
Emission spectrum
The visible light Chlorine emits when energised — its unique spectral fingerprint.
Identity
- Atomic number
- 17
- Standard atomic weight
- 35.45 u
- Category
- Reactive nonmetal
- Group
- 17 · Halogens
- Period
- 3
- Block
- p-block
- Oxidation states
- +7, +5, +1, -1
Physical properties
- Melting point
- 172 K · -102 °C
- Boiling point
- 239 K · -34 °C
- Density
- 3.2 g/cm³
- Molar heat capacity
- —
- Atomic radius
- 175 pm
- Electron affinity
- 348.575 kJ/mol
Atomic structure
17protons
18neutrons
17electrons
7valence e⁻
- Noble-gas notation
- [Ne] 3s2 3p5
- Full configuration
- 1s2 2s2 2p6 3s2 3p5
- Electrons per shell
- 2, 8, 7
Periodic trends
Where Chlorine ranks across all 118 elements.
Ionization energies
Energy to remove each successive electron (kJ/mol).
1.3k1
2.3k2
3.8k3
5.2k4
6.5k5
9.4k6
11.0k7
33.6k8
38.6k9
44.0k10
Successive ionization energies (kJ/mol, log scale).
Discovery
- Discovered
- 1774
- Discovered by
- Carl Wilhelm Scheele
- Named by
- —
- Appearance
- pale yellow-green gas