Interhalogen compounds preparation and properties, Group 17 P Block Elements
Interhalogen Compounds :
→ Halogene have tendency to react with the other members of group 17. This tendency is due to the difference in their electonegativities. These halogens combine with each other and form binary covalent compounds.
→ These compounds are known & interhalogen compounds. These interhalogen compounds are of AB, type where A is always bigger atom with low electronegativity while Bis smaller atom with high electronegativity. Here may be 1, 3, 5 and 7.
Interhalogen compounds are of four type:
- AB type – CIF, BrF, BrCl, ICl, IBr
- AB type – CIF3 BrF3, ICI3
- AB type – BrF5, IF5
- AB type – IF7
The name of these interhalogen compounds is written as:
- The halogen with positive oxidation state is named as such with oxidation number in roman numeral in parenthe
- The halogen with negative oxidation state is named as halide.
- B-C-Bromine (I) chloride
- ICI3 – lodine trichloride or iodine (III) chloride
- IF7 – Iodine heptachloride or iodine (VII) chloride
- ICI5 – Iodine penta chloride or iodine (V) chloride
→ Except IF7 generally all the interhalogen compounds can be prepared by direct combination of hakene under specific conditions. Some preparations are as follows:
Higher interhalogen can also be prepared by reacting lower interhalogen with ha1oens.
Structure of interhalogen compounds
→ AB Type: In this type of interhalogen compounds the bigger halogen atom is sp3 hybridised. It has tetrahedral geometrical linear abape. In tetrahedral geometry three hybrid orbitals contain one lone pair of electron each while the fourth sp3 hybridised orbital overlap with porbital of another halogen. Thus, the shape becomes linear :
→ AB3 Type : In this type of interhalogen compounds the bigger halogen atom is sp3 d hybridised. It has triangular bipyramidal geometry and bent T shape. In sp3 d orbitale two hybrid orbitals have lone pair of electron while other three hybrid orbitals overlap with porbital of halogen atom.
→ AB5 Type : In this type of interhalogen compounds the bigger halogen atom is sp3 d2 hybridised. It has octahedral geometry and square pyramidal shape. In sp3d2 hybridised orbitals one has lone pair of electron while other five hybrid orbitals overlap with porbital of halogen atom.
→ AB7 Type : In this type of interhalogen compounde the bigger halogen atom is sp3d3 hybridised. It has pentagonal hipyramidal shape.
Properties of interhalogen compounds
→ Some important properties of interhalogen compounds are as follows:
- Interhalogen compounds are calent compounds
- Due to abschce of unpaired electrons they are diamagnetle in nature.
- They are very good oxidising agents.
Interhalogen compounds like ClF, BrF, ClF3 IF7 are gases while BrF3, BrF5, IF5 are liquid and ICl, IBr, IF3, ICI3, are solids in nature.
→ Some interhalogen compounds of fluorine are colourless while others are generally coloured. The colour become deeper with increase in molecular weight of compound.
→ The thermal stability of interhalogen compounds of the type AB increases with increase in electronegativity difference between A and B Higher the polarity of bond higher will be thermal stability.
IF > BrF > CIF >ICI > IBe > BrCl (Thermal stability)
→ Interhalogen compounds are more reactive than the constituent halogene because 4-B bond is relatively weaker than AABB bond due to difference in electronegativities. The order of reactivity of some interbelogen compounds are as follows: CIF3 > BrF5 > IF7 > BrF5 > IF5 > BeF (Reactivity order)
→ Interhalogen compounds are generally ionised in liquid state or in solution. For example,
→ Hydrolysis of interhalogen compounds give halogen acid and oxyhalogen acid. The oxyhalogen acid is of bigger halogen atom.
→ Interhalogens react with alkali metal halides forming polyhalides.
- ICl + KBr → K+ [IBrCl]–
- ICl + KCl → K+ [ICl2]–
- ICI3 + KCl → K+ [ICl4]–
- IF5 + CsF → Cs+[IF6]–
- BrCl + CsI → Cs+ [IBrCl]–
- IBr + NaBr → Na+[IBr2]–
→ Interhalogen compounds react with metallic and non metallic oxides as follows:
- 3SiO2 + 4BrF3 → 3SiF4 + 2Br2 + 3O2
- 2WO3 + 4BrF3 → 2WF6 + 2Br2 + 3O2
→ Interhalogen compounds of fluorine behave as good fluorinating agents.
- 3UO2 + 4BrF3 → 3UF4 + 2Br2 + 3O2
- UF4 + ClF3 → UF6 + ClF
→ Important characteristics of interhalogen compounds are summarised in Table 7.14
Important Characteristics of iriterhalogen compounds
Use of Interhalogen compounds
→ Interhalogen compounds can be used.
- As non-aqueous solvents.
- As a good fluorinating agents. For example, BrF3 and ClF3 are used to produce UF6.
U(g) + 3ClF3 → 3ClF + UF6
- Chlorofluorocarbons, known as Preons, are used as refrigerants.
- Freon – 11 is CCl3
- Freon – 12 is CCl2F2
- Freon – 13 is CClF3