Fluorine
diatomic nonmetal · period 2 · group 17 (halogens) · p-block
Fluorine is a chemical element with the symbol F and atomic number 9. It is the lightest halogen and exists at standard conditions as a highly toxic, pale yellow diatomic gas.
What the numbers say
At standard temperature and pressure Fluorine is a gas, sitting in period 2, group 17 of the p-block.
Its melting point of 53 K (-220 °C) is the 107th highest of the 110 elements with a measured value — among the lowest-melting elements.
At 0.002 g/cm³ it is the 91st densest of 96 elements with a quoted density.
Pauling electronegativity is 3.98. Paired with oxygen (3.44) that is a difference of 0.54, which puts the bond polar covalent — oxides here tend to be semiconducting or refractory rather than salt-like.
In the solid state it takes a base-centered monoclinic structure.
First identified in 1886.
Crystal structure
Solid Fluorine adopts a Base-centered Monoclinic arrangement, in the Monoclinic system — axes a ≠ b ≠ c, angles α = γ = 90°, β ≠ 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 F — with DFT formation energy, hull stability and band gap where the provider publishes them.
K 2 · L 7
Properties
| Atomic number | 9 |
|---|---|
| Atomic mass | 18.9984031636 u |
| Series | diatomic nonmetal |
| Group | 17 |
| Period | 2 |
| Block | p-block |
| Phase at STP | Gas |
| Density | 0.002 g/cm³ |
| Melting point | 53.48 K (-220 °C) |
| Boiling point | 85.03 K (-188 °C) |
| Electronegativity (Pauling) | 3.98 |
| Electron configuration | [He] 2s² 2p⁵ |
| Crystal structure | Base-centered Monoclinic |
| Oxidation states | -1 |
| Discovered | 1886 |
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See F in context with all 118 elements.
Working with fluorine in a real design?
Ask the materials chat how F behaves in your alloy system, what it does to weldability, and which grades to look at — with the source of every number named.