Bromine
halogenProperties
| Property | Value |
|---|---|
| Atomic Mass | 79.904 amu |
| Category | halogen |
| Group | 17 |
| Period | 4 |
| Electron Configuration | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p5 |
| Electronegativity | 2.96 (Pauling) |
| Oxidation States | 5, 3, 1, -1 |
| Melting Point | 265.8 K (-7.3 °C) |
| Boiling Point | 332 K (58.9 °C) |
| Density | 3.1028 g/cm³ |
| Discovered By | Antoine Jerome Balard (1826) |
About Bromine
Bromine is the only nonmetal that is liquid at room temperature, and the Greek root of its name — bromos, stench — is not an exaggeration. A sealed ampoule of dark red Br₂ in a fume hood gives off enough vapor pressure (about 23 kPa at 25 °C) that you can watch reddish gas curl out the moment you crack the seal. Synthetically it sits in the sweet spot of halogen reactivity: more selective than chlorine, faster than iodine, and routinely used for electrophilic aromatic substitution, allylic bromination with NBS, and the appel reaction. The Hell-Volhard-Zelinsky α-bromination of carboxylic acids was an undergraduate synthesis exercise for a century. Industrially, brominated flame retardants like decaBDE and TBBPA have been the main commercial outlet since leaded gasoline (which used 1,2-dibromoethane as a scavenger) disappeared in the 1980s. Commercial bromine comes from Dead Sea brines and the Smackover formation under Arkansas, where bromide is oxidized out with Cl₂ and steam-stripped.
Fun Fact
Bromine and mercury are the only two elements that are liquid at standard room temperature — bromine boils at just 58.8 °C, so a warm afternoon in the lab is enough to keep the headspace of a flask thick with reddish vapor.
Common Uses
- Brominated flame retardants (TBBPA, decaBDE) in electronics and textiles
- Methyl bromide and brominated intermediates in pharmaceutical synthesis
- Sodium bromide for hot-tub sanitizing and well-completion brines
- Silver bromide emulsions in traditional photographic film
- Bromine clathrate hydrate energy storage in flow batteries