Bromine (Br)

Bromine and mercury are the only two elements that are liquid at room temperature, and bromine is the only liquid nonmetal — a dense, dark red liquid that gives off a choking orange vapour, which is where its name comes from, the Greek for stench. Tyrian purple, the dye that made Roman senatorial robes so expensive, is a brominated compound extracted from murex sea snails, roughly 10,000 snails per gram. Bromine is a good fire retardant for the same reason CFCs damaged the ozone layer: bromine radicals are very effective at interrupting chain reactions.

Properties

Atomic number

35

Symbol

Br

Standard atomic weight

79.904 u

Category

Halogen

Group

17

Period

4

Block

p-block

Electron configuration

[Ar] 4s² 3d¹⁰ 4p⁵

Electrons per shell

2, 8, 18, 7

Melting point

265.95 K — -7.2 °C — 19.0 °F

Boiling point

331.95 K — 58.8 °C — 137.8 °F

Density

3.11 g/cm³

Electronegativity

2.96 (Pauling)

Oxidation states

-1, +1, +5

Discovered

1826 by Antoine Jérôme Balard

Electron configuration

Full

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁵

Noble gas shorthand

[Ar] 4s² 3d¹⁰ 4p⁵

Shells

K: 2 · L: 8 · M: 18 · N: 7

What it is used for

• Brominated flame retardants in electronics casings and upholstery
• Drilling fluids, as dense zinc and calcium bromide brines
• Silver bromide in photographic film
• Water treatment in hot tubs and cooling towers
• Methyl bromide fumigation, now heavily restricted

Hazards

• Liquid bromine causes severe chemical burns on contact with skin
• The vapour attacks eyes and lungs at low concentrations
• Reacts violently with aluminium and with many organic materials

IUPAC publishes an interval, [79.901, 79.907]; 79.904 is the conventional value.

Neighbours in the table

Group 17

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