Group 17 elements — 'salt formers'
Halogens are five chemical elements in group 17: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). The name comes from Greek 'halos' (salt) and 'genos' (to produce). They are extremely reactive and form salts with metals.
Read in glossaryFluorine is added to toothpaste and water to prevent cavities
Chlorine is used to disinfect pools and drinking water
Silver bromide was used in photographic film
Iodine is essential for thyroid function
Astatine is the rarest natural element — less than 1 gram exists on Earth
All halogens have outer electron configuration ns²np⁵. They lack only one electron to complete the octet, which accounts for their high reactivity.
Halogens are the most reactive nonmetals. Fluorine reacts with almost all substances, chlorine is slightly less active. Reactivity decreases down the group.
Halogens react with water differently. Fluorine decomposes water, chlorine partially dissolves, bromine and iodine are poorly soluble.
Cl₂ + H₂O ⇌ HCl + HOCl| Element | Z | Mass u | M.P. °C | B.P. °C | ρ г/см³ | EN |
|---|---|---|---|---|---|---|
F Fluorine | 9 | 19.00 ▼ | -220 ▼ | -188 ▼ | 0.00 ▼ | 3.98 ▲ |
Cl Chlorine | 17 | 35.45 | -102 | -34 | 0.00 | 3.16 |
Br Bromine | 35 | 79.90 | -7 | 59 | 3.10 | 2.96 |
I Iodine | 53 | 126.90 | 114 | 184 | 4.93 | 2.66 |
At Astatine | 85 | 210.00 | 302 | 337 | 7.00 | 2.20 ▼ |
Ts Tennessine | 117 | 294.21 ▲ | 450 ▲ | 610 ▲ | 7.20 ▲ | — |
The name 'halogens' comes from Greek ἅλς (hals) — 'salt' and γενές (genos) — 'to produce'. These elements form salts when reacting with metals.
Carl Scheele isolated 'dephlogisticated muriatic acid air' — chlorine
Henri Moissan isolated fluorine after 74 years of failed attempts by others
First mass use of chlorine as a weapon in World War I
Roy Plunkett accidentally discovered polytetrafluoroethylene (PTFE)
First isolated pure fluorine, Nobel Prize 1906
Discovered chlorine, oxygen, and many other substances
Accidentally discovered iodine while producing saltpeter