Interhalogen 1165416 175019617 2007-12-01T09:35:37Z Rursus 31073 /* Diatomic interhalogens */ +fix contradiction: IF is not *unknown" if it is treated in next para! The [[halogens]] react with each other to form '''interhalogen''' compounds. The general formula of most interhalogen compounds is XY<sub>n</sub>, where n = 1, 3, 5 or 7 (X is the less [[electronegativity|electronegative]] of the two halogens). [[chlorine trifluoride|ClF<sub>3</sub>]] is used in the manufacture of [[uranium hexafluoride]]. They are all prone to [[hydrolysis]], and [[ionization|ionise]] to give rise to [[polyatomic ion|polyatomic]] [[ion|cations]] and [[ion|anions]]. ==Diatomic interhalogens== 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 bond|ionic]] character, the less [[electronegative]] [[chemical element|element]], X, being oxidised and having a partial positive charge. Most combinations of F, Cl, Br and I are known, but not all are stable. *'''[[Chlorine monofluoride]]''' (ClF), the lightest interhalogen compound, is a colorless gas with a [[normal boiling point]] of −100 °C. *'''[[Bromine monofluoride]]''' (BrF) has not been obtained pure — it dissociates into the trifluoride and free [[bromine]]. Similarly, iodine monofluoride is unstable — [[iodine]] reacts with [[fluorine]] to form a pentafluoride. *'''[[Iodine monofluoride]]''' (IF) is unstable and [[disproportionation|disproportionates]] rapidly and irreversibly at room temperature: 5IF → 2I<sub>2</sub> + [[iodine pentafluoride|IF<sub>5</sub>]]. However, its molecular properties can still be precisely determined by [[spectroscopy]]: the iodine-fluorine distance is 190.9 pm and the I−F [[bond dissociation energy]] is around 277 kJ mol<sup>−1</sup>. [[standard enthalpy change of formation|Δ''H''<sub>f</sub>°]] = −95.4 kJ mol<sup>−1</sup> and [[Gibbs free energy|Δ''G''<sub>f</sub>°]] = −117.6 kJ mol<sup>−1</sup>, both at 298 [[kelvin|K]]. IF can be generated, albeit fleetingly, by the following reactions: I<sub>2</sub> + F<sub>2</sub> →2IF at −45 °C in [[trichlorofluoromethane|CCl<sub>3</sub>F]]; I<sub>2</sub> + [[iodine trifluoride|IF<sub>3</sub>]] → 3IF at −78 °C in CCl<sub>3</sub>F; I<sub>2</sub> + [[silver(I) fluoride|AgF]] → IF + [[silver iodide|AgI]] at 0 °C. *'''[[Bromine monochloride]]''' (BrCl) is a red-brown gas with a boiling point of 5 °C. *'''[[Iodine monochloride]]''' (ICl) consists of red transparent crystals which 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 HICl<sub>2</sub>. The [[crystal structure]] of iodine monochloride consists of puckered zig-zag chains, with strong interactions between the chains. *'''[[Iodine monobromide]]''' (IBr) is made by 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. ==Tetra-atomic interhalogens== *'''[[Chlorine trifluoride]]''' (ClF<sub>3</sub>) is a colourless gas which condenses to a green liquid, and freezes to a white solid. It is made by reacting chlorine with an excess of fluorine at 250° C in a [[nickel]] tube. It reacts more violently than fluorine, often explosively. The molecule is planar and T-shaped. *'''[[Bromine trifluoride]]''' (BrF<sub>3</sub>) is a yellow green liquid which conducts electricity — it ionises to form [BrF<sub>2</sub><sup>+</sup>] + [BrF<sub>4</sub><sup>−</sup>]. It reacts with many metals and metal oxides to form similar ionised entities; with some others it forms the metal fluoride plus free bromine and [[oxygen]]. It is used in [[organic chemistry]] as a fluorinating agent. It has the same molecular shape as chlorine trifluoride. *'''[[Iodine trifluoride]]''' (IF<sub>3</sub>) is a yellow solid which decomposes above −28 °C. It can be synthesised from the elements, but care must be taken to avoid the formation of [[iodine pentafluoride|IF<sub>5</sub>]]. [[fluorine|F<sub>2</sub>]] attacks [[iodine|I<sub>2</sub>]] to yield IF<sub>3</sub> at −45 °C in [[trichlorofluoromethane|CCl<sub>3</sub>F]]. Alternatively, at low temperatures, the fluorination reaction I<sub>2</sub> + 3[[xenon difluoride|XeF<sub>2</sub>]] → 2IF<sub>3</sub> + 3[[xenon|Xe]] can be used. Not much is known about iodine trifluoride as it is so unstable. *'''[[Iodine trichloride]]''' (ICl<sub>3</sub>) forms lemon yellow crystals which can be melted under pressure to a brown liquid. It can be made from the elements at low temperature, or from iodine pentoxide and hydrogen chloride. It reacts with many metal chlorides to form tetrachloriodides, and hydrolyses in water. The molecule is a planar dimer, with each iodine atom surrounded by four chlorine atoms. ==Hexa-atomic interhalogens== *'''[[Bromine pentafluoride]]''' (BrF<sub>5</sub>) is a colourless fuming liquid, made by reacting bromine trifluoride with fluorine at 200° C. It is physically stable, but reacts violently with water and most metals and [[nonmetal]]s. *'''[[Iodine pentafluoride]]''' (IF<sub>5</sub>) is a colourless liquid, made by reacting iodine pentoxide with fluorine, or iodine with silver fluoride. It is highly reactive, even slowly with glass. It reacts with elements, oxides and carbon halides. The molecule has the form of a tetragonal pyramid. ==Octa-atomic interhalogens== *'''[[Iodine heptafluoride]]''' (IF<sub>7</sub>) is a colourless gas. It is made by reacting the pentafluoride with fluorine. IF<sub>7</sub> is chemically inert, having no lone pair of electrons in the valency shell; in this it resembles [[sulfur hexafluoride]]. The molecule is a pentagonal bipyramid. This compound is the only interhalogen compound possible where the larger atom is carrying seven of the smaller atoms. *All attempts to form bromine heptafluoride have met with failure; instead, bromine pentafluoride and fluorine gas are produced. ==Summary of known interhalogens== {| class="wikitable" style="margin: 1em auto 1em auto" ! || F || Cl || Br || I |- | '''F''' || <center>[[fluorine|F<sub>2</sub>]]</center> || bgcolor="grey" | || bgcolor="grey" | || bgcolor="grey" | |- | '''Cl''' || <center>[[chlorine monofluoride|ClF]], [[chlorine trifluoride|ClF<sub>3</sub>]], [[chlorine pentafluoride|ClF<sub>5</sub>]]</center> || <center>[[chlorine|Cl<sub>2</sub>]]</center> || bgcolor="grey" | || bgcolor="grey" | |- | '''Br''' || <center>[[bromine monofluoride|BrF]], [[bromine trifluoride|BrF<sub>3</sub>]], [[bromine pentafluoride|BrF<sub>5</sub>]]</center> || <center>[[bromine monochloride|BrCl]]</center> || <center>[[bromine|Br<sub>2</sub>]]</center> || bgcolor="grey" | |- | '''I''' || <center>[[iodine monofluoride|IF]], [[iodine trifluoride|IF<sub>3</sub>]], [[iodine pentafluoride|IF<sub>5</sub>]], [[iodine heptafluoride|IF<sub>7</sub>]]</center> || <center>[[iodine monochloride|ICl]], [[iodine trichloride|I<sub>2</sub>Cl<sub>6</sub>]]</center> || <center>[[iodine monobromide|IBr]]</center> || <center>[[iodine|I<sub>2</sub>]]</center> |} ==References== * {{Greenwood&Earnshaw}} ==External links== {{commonscat|Interhalogen compounds}} <!-- Added by Ryan Jones. Think we could do with some more description of how the reaction occurs, uses etc. --> [[Category:Interhalogen compounds| ]] [[de:Interhalogenverbindungen]] [[vi:Hợp chất halôgen]] [[zh:互卤化物]]