Structures of Interhalogen Compounds

This article is an easy-to-understand, well-written study material for students of CBSE classes 11th & 12th to prepare for their examinations. The concept of the interhalogen compound is important in chemistry. Through this study material, notes on structures of interhalogen compounds, students will become familiar with the concepts of interhalogen compounds, their preparation, and structures, as well as some examples for a better understanding of the topic. This article on structures of interhalogen compounds is written in a concise and precise manner to help students grasp the concepts easily and focus on their syllabus.

Introduction to interhalogen compounds

• Interhalogen compounds, also known as interhalogens, are formed from the reaction of two different halogens with each other.
• When two or more different halogen atoms react and combine to form a molecule in which no other element except halogens is present, that formed molecule is known as an interhalogen compound.
• Most of the known interhalogen compounds are binary, that is, they comprise two distinct elements (halogens) only.

For example, BrF and IF₇ are commonly known as interhalogen compounds.

• Their composition is generally of four types. They are – XX’, XX’₃, XX’₅, and XX’₇.

Here, X is the less electronegative and larger element forming the central atom, and X’ is the more electronegative and smaller element.

• The more electropositive element is written first, followed by the more electronegative one. The naming of interhalogen compounds follows the same rule.

As the difference between the atomic radii of the two halogens increases, the number of halogen atoms surrounding the central halogen atom also increases. For example, the difference between the atomic radii of iodine (I) and fluorine (F) is very large; hence, there are seven fluorine atoms surrounding the central iodine atom. The resultant interhalogen compound is IF₇.

Preparation and uses of interhalogen compounds

• Preparation

• Interhalogens or interhalogen compounds are prepared in either of the following two ways.

1. By direct combination
2. By action of halogen on lower interhalogen compounds.

• The formed product depends on the specific conditions of the reaction.

For example, Cl₂  +  F₂   🡪 2ClF (Equal volume) (437 K) Br₂+ 3F₂ 🡪 2BrF₃ (diluted with water)

• Uses of interhalogen compounds

• They are good fluorinating agents.
• They can also be used as non-aqueous solvents.
• They contribute to the formation of polyhalides by reacting with alkali metals.

Properties of interhalogen compounds

• Interhalogen compounds are covalent molecules.
• They are diamagnetic.
• Except for some compounds like ClF, a gas, almost all interhalogen compounds are either volatile solids or liquids at 298 K.
• The physical properties of an interhalogen compound lie intermediately between its constituent halogens.
• Their melting and boiling points are higher.
• Their chemical reactions are comparable to their constituent halogens.
• Except for fluorine, all interhalogen compounds are typically more reactive than halogens as the X-X’ bond of interhalogens is weaker than the X-X bond of halogens.
• The interhalogen compounds can be considered electrically neutral polyhalogen complexes.
• Their molecular structures of interhalogen compounds are explained by the VSEPR theory involving the concept of the electron-pair bond.

Structures of interhalogen compounds

• The general structures of interhalogen compounds are such that XX’ molecules are typically linear-shaped, XX’₃ molecules are typically bent ‘T’ shaped (or trigonal bipyramidal), XX’₅ molecules are shaped as square pyramidal, and XX’₇ molecules are shaped as pentagonal bipyramidal.
• Some of the examples of such interhalogen compounds are given below.

• XX’ : CIF , BrF ,BrCl, ICl, IBr
• XX’₃ : ClF₃, BrF₃, ICl₃
• XX’₅ : BrF₅, IF₅
• XX’₇ : IF₇

•  Interhalogen compounds are covalent molecules where the larger and more electropositive halogen forms the central atom.

• The presence of three lone pair electrons distorts the tetrahedral shape of the XX’ molecule to a linear shape.
• In the case of XX’₃ molecules, due to the involvement of sp³ hybridisation in its formation it becomes bent ‘T’ shaped (or trigonal bipyramidal shaped).
• In the case of XX’₅ molecules, due to the involvement of sp³d² hybridisation in its formation, it becomes shaped as a square pyramidal (or octahedral).
• In the case of XX’7 molecules, due to the involvement of sp³d³ hybridisation in its formation it becomes shaped as pentagonal bipyramidal.

Conclusion

Through this article written in a concise and precise manner, students have been provided with study material notes on structures of interhalogen compounds and have become familiarised with the concepts of interhalogen compounds, their preparation, their uses, and structures. They are also provided with some examples to better understand the topic to ace their classes 11th & 12th CBSE exam preparations. This study material follows their syllabus and is designed to provide easy-to-understand and well-written notes for students across the nation with different levels of subject matter knowledge on the topic – structures of interhalogen compounds.