Chlorine

Element 17 on the periodic table, symbol Cl, group 17, period 3.

Chlorine is a chemical element with symbol Cl and atomic number 17. It also has a relative atomic mass of 35.5. Chlorine is in the halogen group (17) and is the second lightest halogen following fluorine.

Appearance: pale yellow-green gas

Properties

Atomic Number: 17
Atomic Mass: 35.4500 u
Group: 17
Period: 3
Block: p-block
Category: Diatomic Non-Metal
State at 25 °C: Gas
Melting Point: 171.6 K · -101.5 °C
Boiling Point: 239.1 K · -34 °C
Density: 3.2 g/L
Atomic Radius: 100 pm
Electronegativity: 3.16
Oxidation States: -1, +1, +3, +5, +7
Abundance in Crust: 145 mg/kg
Discovered: 1774
Discovered By: Carl Wilhelm Scheele

Electron Configuration

[Ne] 3s2 3p5

1s2 2s2 2p6 3s2 3p5

Ionisation Energies (kJ/mol)

1. 1,251.2
2. 2,298
3. 3,822
4. 5,158.6
5. 6,542
6. 9,362
7. 11,018
8. 33,604

Elements near Chlorine

Elements in the same group share the number of outer electrons and behave in similar ways. Elements in the same period share a shell, so they change steadily from left to right.