Halogens6 elements · group 17
The halogens form group 17: fluorine, chlorine, bromine, iodine, astatine and tennessine. The name means 'salt-former', because they react with metals to make salts such as sodium chloride. With seven outer electrons, they are one electron short of a full shell, so they are highly reactive and strongly electronegative. At room temperature fluorine and chlorine are gases, bromine is a liquid and iodine is a solid.
# Properties of halogens
- Seven valence electrons (ns² np⁵)
- Exist as diatomic molecules (F₂, Cl₂, Br₂, I₂)
- React with metals to form salts
- Reactivity decreases down the group
- Used in disinfectants, toothpaste and lamps
# List of halogens
| # | Symbol | Element | Atomic mass | Electron configuration | State at 25 °C | Melting point |
|---|---|---|---|---|---|---|
| 9 | F | Fluorine | 18.998 | [He] 2s² 2p⁵ | gas | 53.53 K |
| 17 | Cl | Chlorine | 35.45 | [Ne] 3s² 3p⁵ | gas | 171.6 K |
| 35 | Br | Bromine | 79.904 | [Ar] 3d¹⁰ 4s² 4p⁵ | liquid | 265.8 K |
| 53 | I | Iodine | 126.9 | [Kr] 4d¹⁰ 5s² 5p⁵ | solid | 386.85 K |
| 85 | At | Astatine | 210 | [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵ | solid | 575 K |
| 117 | Ts | Tennessine | [294] | [Rn] 5f¹⁴ 6d¹⁰ 7s² 7p⁵ | predicted solid | 723 K |
# Halogens FAQ
Which elements are halogens?
There are 6 halogens in this table: Fluorine, Chlorine, Bromine, Iodine, Astatine, Tennessine.
Where are the halogens on the periodic table?
The halogens are found in group 17, the second column from the right.
What are the properties of halogens?
Seven valence electrons (ns² np⁵); Exist as diatomic molecules (F₂, Cl₂, Br₂, I₂); React with metals to form salts; Reactivity decreases down the group; Used in disinfectants, toothpaste and lamps.