page_title: Interhalogen
section_title: Diatomic interhalogens
hierarchical_section_title: Interhalogen / Types of interhalogens / Diatomic interhalogens
context_page_description: An interhalogen compound is a molecule which contains two or more different halogen atoms and no atoms of elements from any other group.
  Most interhalogen compounds known are binary. Their formulae are generally XYₙ, where n = 1, 3, 5 or 7, and X is the less electronegative of the two halogens. The value of "n" in interhalogens is always odd, because of the odd valence of halogens. They are all prone to hydrolysis, and ionize to give rise to polyhalogen ions. Those formed with astatine have a very short half-life due to astatine being intensely radioactive.
  No interhalogen compounds containing three or more different halogens are definitely known, although a few books claim that IFCl
  ₂ and IF
  ₂Cl have been obtained, and theoretical studies seem to indicate that some compounds in the series BrClF
  ₙ are barely stable.
context_section_description: The interhalogens of form XY have physical properties intermediate between those of the two parent halogens. The covalent bond between the two atoms has some ionic character, the less electronegative halogen, X, being oxidised and having a partial positive charge. All combinations of fluorine, chlorine, bromine, and iodine that have the above-mentioned general formula are known, but not all are stable. Some combinations of astatine with other halogens are not even known, and those that are known are highly unstable.
  Chlorine monofluoride (ClF) is the lightest interhalogen compound. ClF is a colorless gas with a normal boiling point of −100 °C.
  Bromine monofluoride (BrF) has not been obtained as a pure compound — it dissociates into the trifluoride and free bromine. It is created according to the following equation:
  Br₂(l) + F₂(g) → 2 BrF(g)
  Bromine monofluoride dissociate like this:
  3 BrF → Br₂ + BrF₃
  Iodine monofluoride (IF) is unstable and decomposes at 0 °C, disproportionating into elemental iodine and iodine pentafluoride.
  Bromine monochloride (BrCl) is a yellow-brown gas with a boiling point of 5 °C.
  Iodine monochloride (ICl) exists as red transparent crystals that melt at 27.2 °C to form a choking brownish liquid (similar in appearance and weight to bromine). It reacts with HCl to form the strong acid HICl₂. The crystal structure of iodine monochloride consists of puckered zig-zag chains, with strong interactions between the chains.
  Astatine monochloride (AtCl) is made either by the direct combination of gas-phase astatine with chlorine or by the sequential addition of astatine and dichromate ion to an acidic chloride solution.
  Iodine monobromide (IBr) is made by the direct combination of the elements to form a dark red crystalline solid. It melts at 42 °C and boils at 116 °C to form a partially dissociated vapour.
  Astatine monobromide (AtBr) is made by the direct combination of astatine with either bromine vapour or an aqueous solution of iodine monobromide.
  Astatine monoiodide (AtI) is made by direct combination of astatine and iodine.
  No astatine fluorides have been discovered yet. Their absence has been speculatively attributed to the extreme reactivity of such compounds, including the reaction of an initially formed fluoride with the walls of the glass container to form a non-volatile product. Thus, although the synthesis of an astatine fluoride is thought to be possible, it may require a liquid halogen fluoride solvent, as has already been used for the characterization of radon fluorides.
  In addition, there exist analogous molecules involving pseudohalogens, such as the cyanogen halides.
caption: Iodine monochloride
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