Chlorine (Cl)
Element 17 · halogen · group 17, period 3
Chlorine is element 17, a halogen in group 17 and period 3. Its electron configuration is [Ne] 3s2 3p5. That leaves 7 valence electrons in the outer shell, with the shells filling 2, 8, 7. It is 1 electron short of a full octet, so it gains them and carries a charge of -1.
- 17 protons
- 7 valence e−
- -1
- p-block
Chlorine Lewis dot structure
Chlorine has 7 valence electrons, so its Lewis symbol carries 7 dots: three pairs and one single dot. The dots go one to a side before any of them pair up, so the unpaired ones show exactly how many bonds the atom tends to form. The ion has gained 1 more to fill its shell, so all 8 are drawn as pairs.
Draw it in the Lewis structure generator →
Properties
| Atomic number | 17 |
|---|---|
| Symbol | Cl |
| Standard atomic weight | 35.45 u |
| Group | 17 |
| Period | 3 |
| Block | p-block |
| Category | halogen |
| Electron configuration | 1s2 2s2 2p6 3s2 3p5 |
| Noble-gas notation | [Ne] 3s2 3p5 |
| Electrons per shell | 2, 8, 7 |
| Valence electrons | 7 |
| Common ionic charge | -1 |
| Electronegativity (Pauling) | 3.16 |
| Protons / electrons | 17 / 17 |
Electron configuration of chlorine
Orbitals fill from the lowest energy upward. Writing that out for chlorine gives 1s2 2s2 2p6 3s2 3p5, which is 1s2 2s2 2p6 3s2 3p5 in plain text.
Everything up to Ne is the same as in that noble gas, so it is usually abbreviated to [Ne] 3s2 3p5. 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 | 5 | 6 |
Chlorine ion charge
Chlorine 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
What is the Lewis dot structure of chlorine?
The symbol Cl with 7 dots, one for each valence electron: three pairs and one single dot. Dots go one to a side before any pair up, the same way electrons fill separate orbitals before sharing one. The Cl- ion is drawn in brackets with all eight, because it has gained 1.
How many valence electrons does chlorine have?
Chlorine has 7 valence electrons. For a main-group element the count is the group number minus 10, and chlorine is in group 17.
What is the electron configuration of chlorine?
1s2 2s2 2p6 3s2 3p5, or [Ne] 3s2 3p5 written from the previous noble gas. Orbitals fill lowest energy first.
What is the charge of chlorine?
Chlorine 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 chlorine have?
A neutral chlorine atom has 17 protons and 17 electrons. Its standard atomic weight is 35.45, so the most common isotope has about 18 neutrons.
Chlorine in Lewis structures
What the configuration above means in practice. Chlorine brings 7 valence electrons to each of these, and the working on every one of them starts by counting exactly that.
Nearby elements
See the ionic charge of every element →