Brome (Br): Bohr Model, Protons, Neutrons & Electrons
Brome is element number 35, a halogen in group 17, period 4. Its atom has 35 protons, 44 neutrons and 35 electrons arranged in 4 shells: 2, 8, 18, 7.
- 35 protons
- 44 neutrons
- 35 electrons
Protons, neutrons and electrons in bromine
Le atomic number of bromine is 35, so every bromine atom has 35 protons. A neutral atom has the same number of electrons, 35. The number of neutrons depends on the isotope: neutrons = mass number − atomic number. For bromine-79, that is 79 − 35 = 44 neutrons. Bromine has 2 stable isotopes, with 44, 46 neutrons.
How to draw the Bohr model of bromine
- Draw the nucleus and write 35 p⁺ et 44 n⁰ inside it.
- Draw the first shell and put 2 electrons on it (the first shell holds at most 2).
- Draw the second shell and put 8 electrons on it.
- Draw the third shell and put 18 electrons on it.
- Draw the fourth shell and put 7 electrons on it.
- Check: 2 + 8 + 18 + 7 = 35 electrons, the same as the number of protons.
From potassium onwards the shells don’t simply fill as 2, 8, 8: the fourth shell starts before the third is full, so the real arrangement above (2, 8, 18, 7) is the one to draw.
Electron configuration
The electron configuration of bromine is [Ar] 4s² 3d¹⁰ 4p⁵. Its 7 outer electrons decide how it reacts: it tends to gain 1 more, forming Br⁻ ions.
Key facts about bromine
| Symbol | Br |
|---|---|
| Atomic number | 35 |
| Relative atomic mass | 79.904 |
| Group · period · block | group 17 · period 4 · p-block |
| Type | Halogène |
| State at 25 °C | liquid |
| Couches électroniques | 2, 8, 18, 7 |
| Electron configuration | [Ar] 4s² 3d¹⁰ 4p⁵ |
| Électrons de valence | 7 |
| Common ion | Br⁻ |
| Electronegativity (Pauling) | 2.96 |
| First ionisation energy | 11.81 eV (1139 kJ/mol) |
| Atomic radius (empirical) | 115 pm |
Où bromine sits on the periodic table
Foire aux questions
How many protons, neutrons and electrons does bromine have?
Bromine has 35 protons and 35 electrons (atomic number 35). Its most common isotope, bromine-79, has 79 − 35 = 44 neutrons.
What is the electron configuration of bromine?
[Ar] 4s² 3d¹⁰ 4p⁵. In shells that is 2, 8, 18, 7.
How many valence electrons does bromine have?
7. Bromine is in group 17, and its outer shell holds 7 electrons.
Where is bromine on the periodic table?
In group 17, period 4, in the p-block. It is a halogen.
