Fluorine (F) — Atomic Number 9

Fluorine is a chemical element with the symbol F and atomic number 9. It is the most reactive of all elements — a pale yellow, highly toxic diatomic gas. It has the highest electronegativity of any element (3.98 on the Pauling scale). The name comes from Latin fluere (“to flow”) — from the mineral fluorite (CaF₂) used as a flux in smelting.

At a Glance

Discovery

Isolated in 1886 by French chemist Henri Moissan by electrolysis of potassium hydrogen fluoride in anhydrous liquid HF. Isolation defeated chemists for over 70 years — many were poisoned or killed attempting it. Moissan won the 1906 Nobel Prize.

Chemical Properties

Fluorine is the strongest oxidising agent. It reacts with nearly all elements, often explosively.

Key Reactions

1. ${\text{H}}_2+{\text{F}}_2\to 2\text{HF}$ (explosive even in the dark)
2. $2\text{Na}+{\text{F}}_2\to 2\text{NaF}$
3. $2{\text{F}}_2+2{\text{H}}_2\text{O}\to 4\text{HF}+{\text{O}}_2$ (fluorine oxidises water)

Compounds & Uses

IGCSE Essentials

1. Most reactive halogen — reactivity decreases down Group 7
2. Pale yellow gas, diatomic (F₂)
3. Forms F⁻ (gains 1 electron → 2,8)
4. Displaces other halogens from their compounds

Sources

• Fluorine — Wikipedia
• Fluorine — Ptable.com
• Fluorine — RSC Periodic Table