(Chemistry Ch-7) 13. Oxoacids of Halogens & Inter-halogen Compounds

Oxoacids of halogen

  • The oxoacids of halogens are listed in the given table.

Halic (I) acid

(Hypohalous acid)

HOF

(Hypofluorous acid)

HOCl

(Hypochlorous acid)

HOBr

(Hypobromous acid)

HOI

(Hypoiodous acid)

Halic (III) acid

(Halous acid)

HOCIO

(Chlorous acid)

Halic (V) acid

(Halic acid)

HOCIO2

(Chloric acid)

HOBrO2

(Bromic acid)

HOIO2

(Iodic acid)

Halic (VII) acid

(Perhalic acid)

HOCIO3

(Perchloric acid)

HOBrO3

(Perbromic acid)

HOIO3

(Periodic acid)

  • The structures of oxoacids of chlorine are as follows:

  • Since fluorine has high electronegativity and small size, it forms only one oxoacid − HOF (hypofluorous acid).

  • Most of the oxoacids are not stable in pure state. They are stable only in aqueous solutions or in the form of their salts.

Interhalogen Compounds

  • Two different halogens react with each other to form interhalogen compounds.

  • General composition − 

  • X = Halogen of larger size

  •  = Halogen of smaller size

  • X is more electropositive than .

  • As the ratio between radii of X and increases, the number of atoms per molecule also increases.

  • Preparation

  • By the direct combination of halogens or by the action of halogen on lower interhalogen compounds

Example:

  • Physical Properties

Some properties of interhalogen compounds are listed in the given table.

Type

Formula

Physical state and colour

ClF

Colourless gas

BrF

Pale brown gas

IF

Very unstable, detected spectroscopically

BrCl

Gas; at room temperature existence as solid is known

ICl

Ruby red solid (α-form)

Grown red solid (β-form)

IBr

Black solid

ClF3

Colourless gas

BrF3

Yellow green liquid

IF3

Yellow powder

ICl3

Orange solid

IF5

Colourless gas, but solid below 77 K

BrF5

Colourless liquid

ClF5

Colourless liquid

IF7

Colourless gas

  • All are covalent in nature.

  • All are diamagnetic in nature.

  • Volatile solids or liquids at 298 K (Exception: ClF is a gas)

  • Physical properties are intermediate between those of constituent halogens. (Exception: m.p and b.p are a little higher than expected)

  • Chemical Properties

  • More reactive than halogens (except F)

Reason − bond in interhalogens is weaker than X − X bond in halogens. (Except F − F bond)

  • Undergo hydrolysis

  • Give halide ion derived from smaller halogen; and a hypohalite (when ), halite (when ), halate (when ), and perhalate (when) anion derived from the larger halogen

Example: 

  • Structures

  • Can be explained on the basis of VSEPR theory

Example: BrF3

  • It has bent T-shape.

  • The central Br atom has seven electrons in the valence shell.

  • Three of these will form electron pair bonds with three F atoms, leaving behind four electrons.

  • Thus, there are three bond pairs and two lone pairs.

  • According to VSEPR theory, lone pair-lone pair and lone pair-bond pair repulsions are greater than bond pair-bond pair repulsions.

  • Hence, to minimise these lone pair-lone pair and lone pair-bond pair repulsions, the BrF3 molecule acquires the shape of slightly bent ‘T’.

  • The given table lists the inter-halogen compounds with their structures.

Type

Formula

Structure

ClF3

Bent T-shaped

BrF3

Bent T-shaped

IF3

Bent T-shaped

ICl3

Bent T-shaped

IF5

Square

pyramidal

BrF5

Square

pyramidal

ClF5

Square

pyramidal

IF7

Pentagonal

bipyramidal

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