Bromine (Br): electron configuration, atomic mass and facts
Bromine (Br) is element 35 of the periodic table, a halogen in period 4, group 17. Its electron configuration is [Ar] 3d10 4s2 4p5, with electrons arranged in shells 2, 8, 18, 7, and its standard atomic weight is 79.904 u.
💡 One of only two elements that are liquid at room temperature.
▶ Watch Bromine’s electrons orbit in the interactive periodic tableBromine at a glance
| Symbol | Br |
|---|---|
| Atomic number | 35 |
| Atomic mass | 79.904 u |
| Category | Halogen |
| Group | 17 |
| Period | 4 |
| Block | p-block |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p5 |
| Noble-gas shorthand | [Ar] 3d10 4s2 4p5 |
| Electrons per shell | 2, 8, 18, 7 |
| Outer-shell electrons | 7 |
| Electronegativity (Pauling) | 2.96 |
| State at 20 °C | liquid |
Where is Bromine on the periodic table?
Bromine is in period 4, group 17, in the p-block. The period number matches its 4 electron shells, and the block names the subshell its last electrons fill. In the same group, Chlorine sits directly above it and Iodine sits directly below it. Elements in one group have the same number of outer-shell electrons (7 here), which is why they react in similar ways.
How to work out the electron configuration of Bromine
Put 35 electrons into subshells in order of rising energy, filling each before starting the next: 1s² (2), 2s² (4), 2p⁶ (10), 3s² (12), 3p⁶ (18), 4s² (20), 3d¹⁰ (30), 4p⁵ (35). In shorthand, [Ar] stands for the 18 electrons of argon, giving [Ar] 3d¹⁰ 4s² 4p⁵.
How electronegative is Bromine?
Bromine has a Pauling electronegativity of 2.96, ranking 6 of the 100 elements with a known value (fluorine is highest at 3.98). That is high: it pulls shared electrons strongly towards itself in a bond.
Bromine in the virtual lab
Faradium’s chemistry workbench includes these chemicals that contain bromine: Sodium bromide, Bromine water. Open the Chemistry Lab to experiment with them.
Frequently asked questions
What is the electron configuration of Bromine?
The electron configuration of Bromine (Br) is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p5. In noble-gas shorthand it is written [Ar] 3d10 4s2 4p5.
How many electrons does Bromine have in each shell?
Bromine has 35 electrons arranged in shells as 2, 8, 18, 7. It has 7 electrons in its outer shell.
What is the atomic mass of Bromine?
The standard atomic weight of Bromine is 79.904 u, so one mole of Bromine atoms has a mass of about 79.904 g.
Is Bromine a metal?
No. Bromine is a halogen.
Explore nearby elements
More halogens: Fluorine, Chlorine, Iodine, Astatine, Tennessine. See all elements on the periodic table.