Atomic Properties of Br
- Atomic Number of Br
- 35
- Atomic Mass of Br
- 79.9040 u
- Electron Configuration
- [Ar] 3d10 4s2 4p5
- Electronegativity
- 2.96
- Block
- p-block
- Group
- 17
- Period
- 4
At room temperature, only two elements are liquids: mercury and bromine. Bromine is the nonmetallic one, a dense red-brown liquid that readily releases an irritating vapor. Its name comes from a Greek word for stench, an honest warning about a substance that damages tissue and belongs inside controlled equipment.
Bromine sits between chlorine and iodine in group 17, and its reactivity falls between them too. In nature it appears as bromide ions, especially in seawater and concentrated brines. Industry oxidizes bromide to produce elemental Br2, reversing the electron gain that normally keeps bromine in its more stable ionic form.
Photography gave bromine an influential role. Silver bromide crystals change when exposed to light, creating a hidden image that chemical development can reveal. Digital sensors displaced most photographic film, but the reaction remains a classic example of light initiating chemistry. Bromine compounds also serve in dyes, disinfectants, medicines, and specialized industrial materials. Some brominated flame retardants slow ignition, although persistence and health concerns have led to restrictions and careful evaluation of particular compounds.
Past uses show why chemical benefits need revision. Ethylene dibromide once helped prevent lead deposits in engines burning leaded gasoline, then both the fuel system and additive were phased out because of their hazards. Some ozone-depleting bromine compounds have likewise been controlled internationally.
Bromine is a Collection Agent visible in motion: a liquid becoming vapor, bromide becoming Br2, and light changing silver bromide. Its chemistry records technology learning not only how to use an element, but when to move on.