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Group 17: Interhalogen Compounds

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Group 17: Interhalogen Compounds - Lesson Summary

Interhalogen compounds are the derivatives of halogens. Compounds containing two different types of halogens are called interhalogen compounds.

Ex: Chlorine monofluoride, bromine trifluoride, iodine pentafluoride, iodine heptafluoride…etc

Types of inter halogen compounds:

Depending on the number of atoms in the molecule interhalogens are classified into four types.

They are

  • AX
  • AX3
  • AX5
  • AX7

'A' is larger (or) less electronegative halogen and 'X' is smaller (or) more electronegative halogen.

Number of atoms in a molecule can be known with the radius ratio.

Radius Ratio = Radius of larger halogen atom / Radius of smaller halogen atom

As the radius ratio increases the number of atoms per molecule also increases. So among interhalogen compounds Iodine heptafluoride has largest no of atoms per molecule as it has highest radius ratio.

Preparations of Interhalogen compounds:

These compounds are prepared by two methods.

By direct combination of Halogens and by reaction of Halogens with lower Interhalogen compounds.

(i) Halogen molecules react directly to form interhalogen compound

Ex: Equal volumes of chlorine and fluorine combine at 473K to form chlorine monofluoride.

(ii) A halogen molecule reacts with a lower interhalogen to form a new interhalogen compound.

Ex: Fluorine reacts with iodine pentafluoride at 543K to form Iodine Heptafluoride

Physical properties:

Interhalogen compounds exist in gaseous state, liquid state (or) solid state.

Most of these compounds are volatile solids (or) liquids at 298K while remaining are gases.

For example chlorine monofluoride is gas while bromine trifluoride and iodine trifluoride are existing in liquid and solid state respectively.

All these compounds are covalent in nature due to less electronegativity difference between bonded atoms.

Ex: Chlorine monofluoride, Bromine trifluoride , Iodine heptafluoride are covalent.

All these compounds are Diamagnetic in nature as they have only lone pairs and bond pairs.

Interhalogen compounds are more reactive than constituent halogens (except fluorine). This is because A-X bond in interhalogens is weaker than X-X bond in halogens except F-F bond.

Structures of these different types of inter halogens are different from one another which can be explained using V.S.E.P.R Theory.

In chlorine trifluoride the central atom chlorine has seven electrons in the valence shell. Three of these will form three bondpairs with three fluorine atoms leaving four electrons.

According to V.S.E.P.R theory these will occupy corners of trigonal bipyramid. The lone pairs will occupy the equatorial positions while bond pairs will occupy the other three positions.

To minimize the lone pair- lone pair repulsions the axial bond pairs will bend towards the equatorial positions. Hence its shape is bent T-shape.

In Iodine pentafluoride the central atom has five bond pairs and one lone pair hence shape is square pyramidal.

In Iodine heptafluoride the central atom has seven bond pairs so it has pentagonal bipyramidal shape.


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