Chemistry · Ch 7 — Elements of Groups 16, 17 and 18

General characteristics of interhalogen compounds

7.12.2

General characteristics of interhalogen compounds

Note

The book prints the number 7.12.1 twice — once for "Classification :" and again for this "General characteristics of interhalogen compounds" heading. To keep every section addressable, this second 7.12.1 is numbered 7.12.2 here; the title is the book's own.

1. The compound is considered as the halide of X. For example, in ClF the halogen having larger size is chlorine — it is more electropositive than F — and hence the interhalogen compound is named as chlorine monofluoride.

2. Interhalogen compounds have an even number of atoms: 2, 4, 6, 8. For example, $\mathrm{ClF_3}$ has 4 atoms.

3. The properties of interhalogen compounds are generally intermediate between those of the halogens from which they are made.

4. The central halogen exhibits different oxidation states in different interhalogen compounds.

5. The number of X′ atoms in the compounds is always odd.

6. They are all diamagnetic.

Note

Do you know ? $\mathrm{XX'}$ compounds are more reactive than $\mathrm{X_2}$ or $\mathrm{X'_2}$ . In the X-X′ bond, X′ is more electronegative than X, while in $\mathrm{X_2}$ and $\mathrm{X'_2}$ both atoms have the same electronegativity; hence the X-X′ bond energy is less than the X-X or X′-X′ bond energy.

Table 7.10 : States of Interhalogen compounds at 25°C

Formula	State
$\mathrm{XX'}$
ClF	Colorless gas
BrF	Pale brown gas
BrCl	Gas
ICl	Ruby red solid ( $\alpha$ - form) / Brown red solid ( $\beta$ - form)
IBr	Black solid
$\mathrm{XX'_3}$
$\mathrm{ClF_3}$	Colorless gas
$\mathrm{BrF_3}$	Yellow green liquid
$\mathrm{IF_3}$	Yellow powder
$\mathrm{ICl_3}$	Orange solid, dimerises to form $\mathrm{I_2Cl_6}$ (having Cl - bridges)
$\mathrm{XX'_5}$
$\mathrm{IF_5}$	Colorless gas at R. T. but solid below 77 K
$\mathrm{BrF_5}$	Colorless liquid
$\mathrm{ClF_5}$	Colorless liquid
$\mathrm{XX'_7}$
$\mathrm{IF_7}$	Colorless gas

(The book's ICl cell prints "Brown red soid" for the $\beta$ -form — the intended word, restored above, is "solid".)

Methods of Preparation of Interhalogen compounds (the book collects these in a table)

Method	$\mathrm{XX'}$	$\mathrm{XX'_3}$
1. Direct combination	Both in equal volumes: $\mathrm{Cl_2 + F_2 \xrightarrow[Cu\text{-}vessel]{523\ K} 2ClF}$ ; $\mathrm{I_2 + Cl_2 \xrightarrow[boil]{HCl + HNO_3} 2ICl}$ ; $\mathrm{Br_2 + Cl_2 \longrightarrow 2BrCl}$	$\mathrm{Cl_2 + 3F_2\,(excess) \longrightarrow 2ClF_3}$ ; $\mathrm{Br_2 + 3F_2 \longrightarrow 2BrF_3}$ ; $\mathrm{I_2 + 3Cl_2\,(excess) \longrightarrow 2ICl_3}$
2. Reaction of halogen with interhalogen compounds.	$\mathrm{Br_2 + BrF_3 \longrightarrow 3BrF}$	$\mathrm{Br_2 + ClF_3 \longrightarrow 2BrF_3 + BrCl}$
Special reaction for ICl	$\mathrm{I_2 + KClO_3 \xrightarrow{\Delta} ICl + KIO_3}$	-------

Note

Do you know ? ICl in the liquid state undergoes autoionization, like water, to form a cation and an anion: $\mathrm{2\,ICl \rightleftharpoons \underset{(solvent\ cation)}{I^{+}} + \underset{(solvent\ anion)}{ICl_2^{-}}}$

Some Properties of Interhalogen compounds (the book collects these in a table)

	Reaction/Property	$\mathrm{XX'}$	$\mathrm{XX'_3}$
1	Thermal stability	ClF > ICl > IBr > BrCl > BrF
2	Hydrolysis gives oxoacids	$\mathrm{BrCl + H_2O \longrightarrow HOBr + HCl}$ ; $\mathrm{5ICl + 3H_2O \longrightarrow HIO_3 + 5HCl + 2I_2}$	$\mathrm{2ICl_3 + 3H_2O \longrightarrow HIO_3 + 5HCl + ICl}$
3	Disproportionation/ Autoionisation	$\mathrm{5BrF \longrightarrow 2Br_2 + BrF_5}$	$\mathrm{2ClF_3 \longrightarrow ClF_2^{+} + ClF_4^{-}}$ ; $\mathrm{ICl_3 \xrightarrow{341\ K} ICl + Cl_2}$
4	Fluorination (the book's row label prints "Flourination")	---------	$\mathrm{U + ClF_3 \longrightarrow UF_6({\it l}) + ClF(g)}$
5	Addition across olefins	$\mathrm{H_2C{=}CH_2 + ICl \longrightarrow CH_2I{-}CH_2Cl}$ (the book draws the product as a 2D structural formula, with I and Cl on the two carbons)

Uses of interhalogen compound (the book collects these in a table)

$\mathrm{XX'}$	$\mathrm{XX'_3}$
ICl is used to determine the iodine value of oils	For Preparation of polyhalides
As catalyst for oxidation of As(III)	As fluorinating agent
For Preparation of polyhalides	As nonaqueous solvent

Table 7.11 Structures of some Interhalogen Compounds

| Formula | Name | Shape |

|---|---|---| …

Figure 7.12.2aThe five structure drawings of Table 7.11: linear Cl-I-Cl as printed for iodine monochloride, bent T-shaped ClF3 with its 89 degree angle, bent T-shaped BrF3 with its 86 degree angle and two lone-pair lobes, and square pyramidal BrF5 and ClF5 each with a lone-pair lobe.

Fig. 7.12.2a — The five structure drawings of Table 7.11: linear Cl-I-Cl as printed for iodine monochloride, bent T-shaped ClF3 with its 89 degree angle, bent T-shaped BrF3 with its 86 degree angle and two lone-pair lobes, and square pyramidal BrF5 and ClF5 each with a lone-pair lobe.

Drawn by us to help you understand the concept clearly, and verified to make sure it's accurate. For exams, practice from your textbook's own diagram.

The Structure column of Table 7.11, drawn out. $\mathrm{ClF_3}$ and $\mathrm{BrF_3}$ are bent T-shaped - the printed angles (89° and 86°, less than 90°) are the squeeze the two equatorial lone pairs put on the bonds. $\mathrm{BrF_5}$ and $\mathrm{ClF_5}$ are square pyramidal, with one lone-pair lobe completing the octahedral arrangement. …

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