Bromine (Br)
Element 35 · Halogen · atomic mass 79.904 u · group 17, period 4
Electron shells: 2, 8, 18, 7
Bromine is one of only two elements that are liquid at room temperature, and it smells appalling. Its compounds were once everywhere as flame retardants before environmental limits tightened.
Bromine and mercury are the only two elements that are liquid at ordinary room temperature.
- Atomic number
- 35
- Atomic mass
- 79.904 u
- Electron configuration
- [Ar] 4s² 3d¹⁰ 4p⁵
- Group · period · block
- 17 · 4 · p
- Oxidation states
- −1, +1, +3, +5
- Electronegativity
- 2.96 (Pauling)
- Melting point
- -7.2 °C
- Boiling point
- 58.8 °C
- Density
- 3.11 g/cm³
- State at 20 °C
- Liquid
- Appearance
- Deep red-brown liquid
- Discovered
- Antoine Jérôme Balard, 1826
35 protons, and 35 electrons when neutral
IUPAC interval [79.901, 79.907]
Halogens
What Bromine is used for
- Flame retardants
- Drilling fluids
- Water treatment
- Pharmaceutical intermediates
Atomic structure of Bromine
A neutral bromine atom has 35 protons and 35 electrons. Its most common isotope carries about 45 neutrons, which is where the mass number 80 comes from. Change the neutron count and you have a different isotope of bromine; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 18, 7. In orbital notation that is [Ar] 4s² 3d¹⁰ 4p⁵, leaving 7 valence electrons in the outer shell — the ones that do the chemistry.
3D electron orbitals
See where Bromine's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Bromine sits in the periodic table
Group 17, one electron short of a full shell, which makes them aggressive oxidisers. They form salts directly with metals — "halogen" literally means salt-former.
Discovery and naming
Bromine was discovered by Antoine Jérôme Balard in 1826. Its name comes from Greek bromos, "stench".
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Bromine?
The standard atomic weight of Bromine is 79.904 u. Because the natural isotope mix varies between sources, IUPAC publishes it as the interval [79.901, 79.907], and 79.904 is the conventional single value to use in calculations.
How many protons, neutrons and electrons does Bromine have?
Bromine has 35 protons, because the atomic number is the proton count and that is what makes an atom Bromine at all. A neutral Bromine atom has the same number of electrons, 35. The neutron count varies by isotope; the most common one has about 45, since 80 − 35 = 45.
What is the electron configuration of Bromine?
The electron configuration of Bromine is [Ar] 4s² 3d¹⁰ 4p⁵. Its electrons are arranged 2, 8, 18, 7 across 4 shells.
Is Bromine a metal?
No. Bromine is classified as a halogen, on the right-hand side of the table where elements gain or share electrons rather than losing them.
What group and period is Bromine in?
Bromine is in group 17 (the halogens), period 4, in the p-block. The group is its column and the period is its row.
What is the charge of Bromine?
Bromine most commonly forms a 1− ion. It is 1 electron short of a full outer shell, so it gains one rather than losing 7. Across all its compounds it shows oxidation states of −1, +1, +3, +5.
What is the melting point of Bromine?
Bromine melts at -7.2 °C and boils at 58.8 °C. That puts it in the short list of elements that are liquid at room temperature at everyday temperatures.
What is Bromine used for?
Flame retardants, Drilling fluids, Water treatment, Pharmaceutical intermediates. Bromine is one of only two elements that are liquid at room temperature, and it smells appalling.
Who discovered Bromine, and where does its name come from?
Bromine (Br) was discovered by Antoine Jérôme Balard in 1826. The name comes from Greek bromos, "stench".