Chlorine
diatomic nonmetal · period 3 · group 17 (halogens) · p-block
Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them.
What the numbers say
At standard temperature and pressure Chlorine is a gas, sitting in period 3, group 17 of the p-block.
Its melting point of 172 K (-102 °C) is the 100th highest of the 110 elements with a measured value — mid-range among the elements.
At 0.003 g/cm³ it is the 89th densest of 96 elements with a quoted density.
Pauling electronegativity is 3.16. Paired with oxygen (3.44) that is a difference of 0.28, which puts the bond essentially covalent, so the oxide behaves as a molecular or network solid.
In the solid state it takes a base orthorhombic structure.
It is reported in 8 oxidation states (-1, 1, 2, 3, 4, 5, 6, 7), which sets how many distinct compounds and phases it can form.
First identified in 1774.
Crystal structure
Solid Chlorine adopts a Base Orthorhombic arrangement, in the Orthorhombic system — axes a ≠ b ≠ c, angles α = β = γ = 90°. Symmetry controls the anisotropy of stiffness and thermal expansion, and the available slip systems set how far the metal deforms before it fractures.
Check it against computed structures
The structure search queries the Materials Project, OQMD and the Open Materials Database for computed crystal structures containing Cl — with DFT formation energy, hull stability and band gap where the provider publishes them.
K 2 · L 8 · M 7
Properties
| Atomic number | 17 |
|---|---|
| Atomic mass | 35.45 u |
| Series | diatomic nonmetal |
| Group | 17 |
| Period | 3 |
| Block | p-block |
| Phase at STP | Gas |
| Density | 0.003 g/cm³ |
| Melting point | 171.6 K (-102 °C) |
| Boiling point | 239.11 K (-34 °C) |
| Electronegativity (Pauling) | 3.16 |
| Electron configuration | [Ne] 3s² 3p⁵ |
| Crystal structure | Base Orthorhombic |
| Oxidation states | -1,1,2,3,4,5,6,7 |
| Discovered | 1774 |
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See Cl in context with all 118 elements.
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