ElementsWhat are the halogens?
The halogens fill column 17. The name means 'salt former', because they combine with metals to make salts, such as sodium chloride. Each atom needs one more electron to fill its outer shell, so the halogens are very reactive, most of all fluorine at the top. At room temperature the family includes gases (fluorine, chlorine), a liquid (bromine) and a solid (iodine). They are used to disinfect water, and all are harmful in pure form.
The family in numbers
Melting points in this family run from -219.6 °C (fluorine) to 301.9 °C (astatine). Among its solid members, the least dense is iodine (4.93 g/cm³) and the densest is astatine (7 g/cm³). The most recently discovered member is tennessine (2010).
All halogens compared
| No. | Symbol | Name | Atomic mass | State | Melts at | Boils at | Density g/cm³ | Discovered |
|---|---|---|---|---|---|---|---|---|
| 9 | F | Fluorine | 18.99840316 | Gas | -219.6 °C | -188.1 °C | 0.001696 | 1886 |
| 17 | Cl | Chlorine | 35.45 | Gas | -101.5 °C | -34 °C | 0.003214 | 1774 |
| 35 | Br | Bromine | 79.90 | Liquid | -7.2 °C | 58.8 °C | 3.11 | 1826 |
| 53 | I | Iodine | 126.9045 | Solid | 113.7 °C | 184.4 °C | 4.93 | 1811 |
| 85 | At | Astatine | 209.98715 | Solid | 301.9 °C | no value | 7 | 1940 |
| 117 | Ts | Tennessine | 294.211 | Solid | no value | no value | no value | 2010 |
Other families: alkali metals, alkaline earth metals, transition metals, post-transition metals, metalloids, nonmetals, noble gases, lanthanides, actinides.