Bromine · element 35
The only non-metal that is a liquid at room temperature, and it smells exactly as bad as its name suggests
Key facts
Open a bottle of bromine and a heavy red-brown vapour rolls out over the rim. The liquid beneath is dark, dense and almost black in bulk, and the smell is sharp enough that the element was named from the Greek word for stench. Only two elements are liquid at ordinary room temperature, and bromine is the one that is not a metal.
Bromine is a halogen, sitting in group 17 between chlorine and iodine. It is reactive, but less fiercely so than chlorine, and it exists as two-atom molecules just like its neighbours. Most people meet it indirectly, in hot tub sanitisers, in the flame retardants inside their electronics, and historically in the film that captured their family photographs.
Where it is found
Bromine is never found free in nature. It exists as bromide ions dissolved in seawater, at about 65 milligrams per litre, and far more concentrated in salt lakes and underground brines. The Dead Sea and deep brine wells in Arkansas are the two largest sources, with Israel, Jordan, the United States and China as the main producers.
Extraction is straightforward chemistry. Chlorine gas is bubbled through the brine and takes electrons from the bromide ions, releasing bromine, which is then swept out with air or steam and condensed. Living things also make bromine compounds: the ancient purple dye of Tyre, worn by Roman emperors, is a bromine-containing molecule extracted from sea snails.
How it was discovered
Antoine-Jérôme Balard was a 23-year-old assistant at a pharmacy school in Montpellier in 1826, studying the brine left behind in local salt marshes. When he added chlorine, a yellow-brown layer appeared. He suspected it might be a compound of iodine or chlorine, but careful tests showed it was a new element. He announced it to the French Academy of Sciences, which suggested the name bromine.
A German student, Carl Löwig, had isolated the same substance from a mineral spring in 1825 but delayed publishing while finishing his studies. Balard's paper appeared first and the credit went to him. Bromine's properties fitted neatly between chlorine and iodine, a pattern that later helped Mendeleev arrange the table.
What we use it for
For most of the twentieth century the biggest consumer of bromine was leaded petrol, in which ethylene dibromide swept lead out of engines as a vapour. Photographic film relied on light-sensitive silver bromide. Unleaded fuel and digital cameras ended both markets.
Today the largest uses are flame retardants and drilling fluids. Brominated compounds mixed into plastics and foams slow the spread of fire in electronics casings, circuit boards and furniture. Dense solutions of calcium and zinc bromide are pumped into oil and gas wells to control pressure. Bromine compounds sanitise hot tubs and swimming pools, appear in several medicines and pesticides, and are being developed for zinc-bromine flow batteries that store renewable electricity.
Reading the numbers
Bromine melts at about minus 7 °C and boils at 59 °C, so it stays liquid across the whole range of everyday temperatures but would boil in a pan of water well before the water did. Its density of 3.10 grams per cubic centimetre makes it three times heavier than water, a dense liquid that sinks straight to the bottom. The atomic mass of 79.9 is an average of two isotopes, bromine-79 and bromine-81, which occur in almost equal amounts.
The configuration [Ar] 3d10 4s2 4p5 shows seven outer electrons, one short of a full shell. That single vacancy drives everything: bromine grabs an electron to become the bromide ion, or shares one with a second bromine atom to form Br2. Its electronegativity of 2.96 sits between chlorine and iodine, and its first ionisation energy of 1139.9 kJ/mol is high, as expected for an element near the right-hand end of period 4. Being larger than chlorine, bromine holds its electrons more loosely, so it is the less aggressive oxidiser of the two.
Safety and the environment
Liquid bromine causes severe burns and the vapour damages the eyes and lungs, so it is handled in fume cupboards with protective gloves. Bromide ions are far less hazardous and occur naturally in the body, but large doses taken over time cause bromism, confusion and skin eruptions, common when bromide sedatives were prescribed in the nineteenth century.
Some brominated flame retardants persist in the environment and accumulate in fat, and several have been banned under international agreements. Methyl bromide, once a widely used soil fumigant, destroys stratospheric ozone and has been phased out under the Montreal Protocol. Atom for atom, bromine is many times more destructive to ozone than chlorine.
Did you know?
- Bromine and mercury are the only two elements that are liquid at normal room temperature and pressure.
- Balard was 23 years old when he identified bromine in salt marsh brine.
- Bromine's two stable isotopes are so evenly split that its atomic mass comes out almost exactly at 80.
- The imperial purple dye of ancient Rome, made from thousands of sea snails, is a bromine compound.
- The word bromide for a dull, soothing platitude comes from the potassium bromide sedatives that were once handed out freely.
- For decades the biggest use of bromine was in leaded petrol, where it helped carry lead out through the exhaust.
More in the halogens
These share a column with bromine, so their outer electrons are arranged in a similar way and they tend to behave alike.
See all 6 halogens on one page, or browse all 118 elements.
Compare Bromine with another element
Each comparison has a side-by-side data table and a plain-English summary of the differences.
Frequently asked questions
Why is bromine a liquid at room temperature?
Bromine molecules are heavier and have more electrons than chlorine molecules, so the weak attractions between them are stronger and hold them together as a liquid rather than a gas. Iodine, one row further down, has stronger attractions still and is a solid. Bromine happens to fall in the window where it melts below room temperature but boils above it.
Is bromine dangerous?
Elemental bromine is corrosive and its vapour is toxic, causing burns and lung damage, so it is strictly a laboratory and industrial chemical. Bromide compounds used in pools and hot tubs are much safer when used as directed. Some brominated flame retardants have been restricted because they build up in the environment.
Is bromine better than chlorine for hot tubs?
Bromine sanitisers remain effective at the higher temperatures and pH levels found in hot tubs, and they produce less of the sharp smell associated with chlorine. They are more expensive and break down faster in sunlight. Many hot tub owners prefer bromine; pool owners usually stick with chlorine.
What does bromine smell like?
Bromine has a harsh, choking smell often compared to chlorine bleach but heavier and more irritating. The name comes from the Greek bromos, meaning stench. Even small amounts of the vapour are unpleasant and can be detected long before harmful concentrations are reached.
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Written by Anthony. Updated September 2026. Numerical data from Periodic-Table-JSON (CC BY-SA), cross-checked against the Bromine reference article. Spotted an error? Tell us.