---
title: "Fluorine (F) — element 9"
description: "Fluorine is element 9, symbol F, atomic weight 18.998. Configuration, properties, uses and neighbours."
url: https://atoneplace.net/element/fluorine/
site: "At One Place"
---

# Fluorine (F)

**Fluorine — element 9: F**

18.998 u · Halogen · period 2, group 17

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

| Z | Element | Symbol | Mass |
| --- | --- | --- | --- |
| 7 | Nitrogen | N | 14.007 |
| 8 | Oxygen | O | 15.999 |
| 9 | Fluorine ← | F | 18.998 |
| 10 | Neon | Ne | 20.18 |
| 11 | Sodium | Na | 22.99 |

## 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.

## Common questions

### What is the atomic number of fluorine?

9. That is the number of protons in its nucleus, which is what defines the element.

### What is the symbol for fluorine?

F.

### What is the electron configuration of fluorine?

1s² 2s² 2p⁵, or [He] 2s² 2p⁵ in noble-gas shorthand.

### What is the melting point of fluorine?

53.53 K — -219.6 °C — -363.3 °F

## Related pages

- [Nitrogen (N)](https://atoneplace.net/element/nitrogen/)
- [Oxygen (O)](https://atoneplace.net/element/oxygen/)
- [Neon (Ne)](https://atoneplace.net/element/neon/)
- [Sodium (Na)](https://atoneplace.net/element/sodium/)
- [Chlorine (Cl)](https://atoneplace.net/element/chlorine/)
- [Bromine (Br)](https://atoneplace.net/element/bromine/)
- [Iodine (I)](https://atoneplace.net/element/iodine/)
- [Astatine (At)](https://atoneplace.net/element/astatine/)
- [Tennessine (Ts)](https://atoneplace.net/element/tennessine/)

## Sources

- Official vendor product documentation — At One Place (/about/)