Bromine

The only nonmetal that is a liquid at room temperature: dark red, heavy, fuming, and named for its smell.

In nature it is never aloneBr₂Read about the molecule

At a glance

Symbol: Br
Atomic number: 35
Average atomic mass: 79.90
Group: 17
Period: 4
Family: halogen
Electron configuration: [Ar] 3d¹⁰ 4s² 4p⁵
Valence electrons: 7
Electronegativity: 2.96
Common ions: Br⁻ (bromide), as in NaBr and AgBr
Isotopes: ⁷⁹Br (50.7%) and ⁸¹Br (49.3%), an almost even split

On the table

Period 4, group 17: the third rung down the stem of the 7. The other halogens are tinted, and every cell opens its own article.

Why it pairs up

Seven valence electrons, one short of eight. Two bromine atoms share one pair, a single bond.

Properties

State at 25 °C: liquid
What it looks like: dark red-brown liquid made of Br₂ molecules, giving off red-brown vapor
Melting point: −7.2 °C
Boiling point: 58.8 °C
Density: 3.11 g/cm³

Where it is found

Rare in rock, about 0.0004% of the crust, but seawater holds about 65 mg of bromide per liter and some brines hold far more. The Dead Sea and the deep brines under Arkansas and Michigan are the main sources.

Discovery and name

Antoine Jérôme Balard, a 23-year-old pharmacy student in Montpellier, isolated it from salt-marsh brine in 1826. Carl Löwig had found it a year earlier in Germany but published later. The name is from the Greek bromos, stench.

What it is used for

Bromine compounds make flame retardants for plastics and electronics, dense drilling fluids for oil wells, pool and spa sanitizers, and some medicines and dyes. Silver bromide was the light-sensitive layer of photographic film.

In compounds

NaBrsodium bromideAgBrsilver bromide, photographic filmKBrpotassium bromide, an early sedativeCaBr₂calcium bromide, a heavy drilling fluidCH₃Brmethyl bromide, a fumigantHBrhydrobromic acid