Fluorine (F)

Fluorine is the most electronegative element, which makes it the most reactive: it attacks glass, sets asbestos alight, and burns in an atmosphere of chlorine. Isolating it killed or maimed several nineteenth-century chemists before Moissan managed it by electrolysis in 1886, and the group are still known as the fluorine martyrs. The C-F bond that results is the strongest single bond carbon forms, which is why Teflon is inert and why PFAS "forever chemicals" persist in the environment for decades.

Properties

Atomic number

9

Symbol

F

Standard atomic weight

18.998 u

Category

Halogen

Group

17

Period

2

Block

p-block

Electron configuration

[He] 2s² 2p⁵

Electrons per shell

2, 7

Melting point

53.53 K — -219.6 °C — -363.3 °F

Boiling point

85.03 K — -188.1 °C — -306.6 °F

Density

0.001696 g/cm³

Electronegativity

3.98 (Pauling)

Oxidation states

-1

Discovered

1886 by Henri Moissan

Electron configuration

Full

1s² 2s² 2p⁵

Noble gas shorthand

[He] 2s² 2p⁵

Shells

K: 2 · L: 7

What it is used for

• PTFE (Teflon) on non-stick pans and in chemical plant seals
• Uranium enrichment, as uranium hexafluoride
• Fluoride in toothpaste and drinking water
• Sulfur hexafluoride as an insulating gas in high-voltage switchgear
• Roughly a fifth of all pharmaceuticals contain a fluorine atom

Hazards

• Fluorine gas reacts violently with almost every material including water
• Hydrofluoric acid penetrates skin painlessly and destroys bone; a spill the size of a palm can be fatal
• Fluoride is beneficial in parts per million and toxic in grams

Density is the gas at 0 °C and 101.325 kPa. Fluorine has only one stable isotope, so its atomic weight is known to eleven digits — 18.998403162 — one of the most precisely determined in the table.

Neighbours in the table

Group 17

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Fluorine sits in group 17 with chlorine, bromine, iodine, astatine, tennessine.