Chlorine (Cl): Bohr Model, Protons, Neutrons & Electrons
Chlorine is element number 17, a halogen in group 17, period 3. Its atom has 17 protons, 18 neutrons and 17 electrons arranged in 3 shells: 2, 8, 7.
Protons, neutrons and electrons in chlorine
The atomic number of chlorine is 17, so every chlorine atom has 17 protons. A neutral atom has the same number of electrons, 17. The number of neutrons depends on the isotope: neutrons = mass number − atomic number. For chlorine-35, that is 35 − 17 = 18 neutrons. Chlorine has 2 stable isotopes, with 18, 20 neutrons.
How to draw the Bohr model of chlorine
- Draw the nucleus and write 17 p⁺ and 18 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 7 electrons on it.
- Check: 2 + 8 + 7 = 17 electrons, the same as the number of protons.
Electron configuration
The electron configuration of chlorine is [Ne] 3s² 3p⁵. Its 7 outer electrons decide how it reacts: it tends to gain 1 more, forming Cl⁻ ions.
Key facts about chlorine
| Symbol | Cl |
|---|---|
| Atomic number | 17 |
| Relative atomic mass | 35.45 |
| Group · period · block | group 17 · period 3 · p-block |
| Type | Halogen |
| State at 25 °C | gas |
| Electron shells | 2, 8, 7 |
| Electron configuration | [Ne] 3s² 3p⁵ |
| Valence electrons | 7 |
| Common ion | Cl⁻ |
| Electronegativity (Pauling) | 3.16 |
| First ionisation energy | 12.97 eV (1251 kJ/mol) |
| Atomic radius (empirical) | 100 pm |
Where chlorine sits on the periodic table
Frequently asked questions
How many protons, neutrons and electrons does chlorine have?
Chlorine has 17 protons and 17 electrons (atomic number 17). Its most common isotope, chlorine-35, has 35 − 17 = 18 neutrons.
What is the electron configuration of chlorine?
[Ne] 3s² 3p⁵. In shells that is 2, 8, 7.
How many valence electrons does chlorine have?
7. Chlorine is in group 17, and its outer shell holds 7 electrons.
Where is chlorine on the periodic table?
In group 17, period 3, in the p-block. It is a halogen.
