Bromine (Br): Electron Configuration, Properties and Uses
Bromine (Br): Electron Configuration, Properties and Uses
Electron configuration [Ar] 4s2 3d10 4p5 · group 17 · period 4 · Ar 79.904
Bromine data
- Atomic number
- 35
- Relative atomic mass
- 79.904
- Group
- 17
- Period
- 4
- Block
- p
- Category
- Halogen
- Electron configuration
- [Ar] 4s2 3d10 4p5
- Full configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5
- Electrons per shell
- 2, 8, 18, 7 (K L M N)
- Valence electrons
- 7
- Electronegativity (Pauling)
- 2.96
- First ionisation energy
- 11.814 eV
- Atomic radius (van der Waals)
- 183 pm
- State at room temperature
- Liquid
- Melting point
- −7.2 °C
- Boiling point
- 58.8 °C
- Density
- 3.11 g/cm³
- Common oxidation states
- +5, +1, −1
- Discovered
- 1826
Source: PubChem (NIH, accessed 13 Nov 2026); atomic mass: IUPAC standard atomic weight.
Electron shell diagram
K 2 · L 8 · M 18 · N 7
Orbital diagram (outer electrons)
About bromine
Bromine, symbol Br, is element number 35 in the periodic table. It is a halogen in group 17, period 4, p-block. The element was discovered in 1826. Bromine is one of only two elements that are liquid at room temperature, the other being mercury.
Bromine electron configuration
The electron configuration of bromine is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5, or in short [Ar] 4s2 3d10 4p5. Its electrons occupy 4 shells: K = 2, L = 8, M = 18, N = 7. Bromine has 7 valence electrons in the N shell (4s2 4p5), which is why it sits in group 17. In ionic compounds bromine gains electrons to fill its outer shell: Br− = [Kr] (like krypton).
Filling order: 1s2(2) → 2s2(4) → 2p6(10) → 3s2(12) → 3p6(18) → 4s2(20) → 3d10(30) → 4p5(35)
Uses of bromine
Well-known applications of bromine include flame retardants, drilling fluids, pharmaceuticals and bromination reagents for organic synthesis. For research and analysis you can browse bromide compounds in the AMI Scientific catalogue.
Safety
Bromine is a highly corrosive liquid with toxic vapour; handle it only in a fume hood with suitable gloves. Always read the safety data sheet (SDS) before working with a chemical.
Other elements in group 17
Frequently asked questions
What is the electron configuration of bromine?
The electron configuration of bromine (Br, atomic number 35) is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5, or [Ar] 4s2 3d10 4p5 in short. By shell: 2, 8, 18, 7.
How many valence electrons does bromine have?
Bromine has 7 valence electrons.
Which group and period is bromine in?
Bromine is in group 17, period 4, p-block.
What is the atomic mass of bromine?
The relative atomic mass of bromine is 79.904. Use it to calculate molar mass with the molar mass calculator.
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