Bromine (Br)
Element 35 · halogen · group 17, period 4
Bromine is element 35, a halogen in group 17 and period 4. Its electron configuration is [Ar] 3d10 4s2 4p5. That leaves 7 valence electrons in the outer shell, with the shells filling 2, 8, 18, 7. It is 1 electron short of a full octet, so it gains them and carries a charge of -1.
- 35 protons
- 7 valence e−
- -1
- p-block
Properties
| Atomic number | 35 |
|---|---|
| Symbol | Br |
| Standard atomic weight | 79.904 u |
| Group | 17 |
| Period | 4 |
| Block | p-block |
| Category | halogen |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p5 |
| Noble-gas notation | [Ar] 3d10 4s2 4p5 |
| Electrons per shell | 2, 8, 18, 7 |
| Valence electrons | 7 |
| Common ionic charge | -1 |
| Electronegativity (Pauling) | 2.96 |
| Protons / electrons | 35 / 35 |
Electron configuration of bromine
Orbitals fill from the lowest energy upward. Writing that out for bromine gives 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p5, which is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p5 in plain text.
Everything up to Ar is the same as in that noble gas, so it is usually abbreviated to [Ar] 3d10 4s2 4p5. The part outside the bracket is what does the chemistry.
| Subshell | Electrons | Capacity |
|---|---|---|
| 1s | 2 | 2 |
| 2s | 2 | 2 |
| 2p | 6 | 6 |
| 3s | 2 | 2 |
| 3p | 6 | 6 |
| 3d | 10 | 10 |
| 4s | 2 | 2 |
| 4p | 5 | 6 |
Bromine ion charge
Bromine commonly forms ions with a charge of -1.
It has 7 valence electrons, so it is 1 short of a full octet and 7 above an empty outer shell. An atom takes whichever route is shorter, which is why the charge comes out as it does.
Common questions
How many valence electrons does bromine have?
Bromine has 7 valence electrons. For a main-group element the count is the group number minus 10, and bromine is in group 17.
What is the electron configuration of bromine?
1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p5, or [Ar] 3d10 4s2 4p5 written from the previous noble gas. Orbitals fill lowest energy first.
What is the charge of bromine?
Bromine commonly forms ions with a charge of -1. With 7 valence electrons it is 1 short of an octet and 7 above an empty shell, so it takes whichever route is shorter.
How many protons, electrons and neutrons does bromine have?
A neutral bromine atom has 35 protons and 35 electrons. Its standard atomic weight is 79.904, so the most common isotope has about 45 neutrons.
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