Halogens are nonmetals. At room temperature, fluorine and chlorine are gases and bromine is a liquid. Iodine and astatine are solids. Halogens are very reactive, the reactivity decreases from fluorine to astatine. Halogens do not exist in the elemental form in nature. Astatine isotopes are radioactive with short half-lives.

Table salt, bleach, fluoride in toothpaste, chlorine in swimming pools, what do all of these have in common? Add halogen lamps to the list, and the answer becomes more clear: all involve one or more of the halogens, which form Group 7 of the periodic table, which consists of five chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). The word ‘halogen’ is derived from Greek and originally means “salt-forming“. Halogens are found in the environment only in the form of ions or compounds, because of their high reactivity.

Physical Properties

  • The group of halogens is the only periodic table group which contains elements in all three familiar states of matter at standard temperature and pressure
  • Fluorine (F) is a pale yellow gas
  • Chlorine (Cl) is a greenish gas
  • Bromine (Br) is a dark red liquid
  • Iodine (I) is a black solid and when heated it forms a purple vapour
  • Astatine (At) is a black solid
  • The halogens all have a strong and often nasty smell
  • The halogen elements are extremely toxic
  • Poor conductors of heat and electricity
  • Low melting and boiling points

Chemical Properties


  • Molecules of all halogens are diatomic. What this means is that their molecules exist with two atoms each.
  • Halogens have seven valence electrons because halogens have one electron missing, they form negative ions and are highly reactive
  • They can gain an electron by reacting with atoms of other elements

Fluorine is one of the most reactive elements in existence

Practise This Question

Out of these, which cannot be maximum capacity of a shell?