Bromine (Br)
Bromine is element 35, a halogen in group 17, period 4. A neutral atom has 35 protons, 45 neutrons and 35 electrons, 7 of them valence electrons.
Halogen- Atomic number
- 35
- Atomic mass
- 79.9 u
- Valence electrons
- 7
- Protons · neutrons
- 35 · 45
- Electrons per shell
- 2, 8, 18, 7
- At room temperature
- liquid
Bohr model of bromine
The Bohr model draws bromine as a nucleus of 35 protons and 45 neutrons, with its 35 electrons on 4 circular shells: 2 in shell 1, 8 in shell 2, 18 in shell 3, 7 in shell 4. Press Build the atom to watch the shells fill from the inside out. The outer ring (the N shell) is dashed: the electrons there are the ones that take part in chemistry.
Real electrons don't travel in neat circles. They live in fuzzy orbitals, shown below, but the Bohr picture is the quickest way to count shells and valence electrons.
Electron configuration of bromine
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁵
Short form (noble gas notation): [Ar] 4s² 3d¹⁰ 4p⁵. The [Ar] stands for the electrons of argon, the noble gas before it.
How many valence electrons does bromine have?
Bromine has 7 valence electrons.
Bromine is in group 17, and for groups 13–18 you subtract 10 from the group number: 17 − 10 = 7. It tends to gain 1 electron to complete an octet, forming a −1 ion.
Protons, neutrons and electrons
| Protons | 35 | equal to the atomic number |
|---|---|---|
| Electrons | 35 | equal to the protons in a neutral atom |
| Neutrons | 45 | mass number 80 − 35 protons |
Atoms of the same element can have different numbers of neutrons (isotopes). The count above uses the rounded atomic mass, the way it's taught in class.
Bromine properties
| Symbol | Br |
|---|---|
| Category | Halogen |
| Group · period · block | 17 · 4 · p |
| Atomic mass | 79.9 u |
| State at 25 °C | liquid |
| Melting point | 265.9 K (-7.2 °C, 19 °F) |
| Boiling point | 331.9 K (58.8 °C, 138 °F) |
| Density | 3.11 g/cm³ |
| Electronegativity (Pauling) | 2.96 |
| Atomic radius | 183 pm |
| First ionization energy | 11.814 eV |
| Electron affinity | 3.365 eV |
| Oxidation states | +5, +1, −1 |
| Common ion charge | −1 |
| Discovered | 1826 by Antoine Jérôme Balard |
Where bromine sits on the periodic table
Group 17: Fluorine, Chlorine, Iodine, Astatine, Tennessine.
Questions about bromine
How many valence electrons does bromine have?
Bromine has 7 valence electrons.
How many protons, neutrons and electrons does bromine have?
A neutral bromine atom has 35 protons and 35 electrons. Its most common form has about 45 neutrons (mass number 80 − 35 protons).
What is the electron configuration of bromine?
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁵, written in short form as [Ar] 4s² 3d¹⁰ 4p⁵.
What does the Bohr model of bromine look like?
A nucleus of 35 protons and 45 neutrons, circled by 4 electron shells holding 2, 8, 18, 7 electrons.
What is the atomic number of bromine?
35. The atomic number is the number of protons in the nucleus, and it is what makes an atom bromine.