Interhalogens and Pseudohalogens

1. INTERHALOGENS
AND
PSEUDOHALOGENS

2. INTERHALOGEN COMPOUNDS
• When two different halogens react with each other, interhalogen
compounds are formed.
• In general, XYn where n=1 , 3 , 5 , 7
X is halogen atom which is less electronegative and larger in size.
Y is halogen atom which is more electronegative than X and smaller in
size.

3. INTERHALOGEN COMPOUNDS
• The interhalogen compounds can be grouped into four categories :
1) XY : ClF , BrF , BrCl , ICl , IBr
2) XY3: ClF3 , BrF3 , IF3 , ICl3
3) XY5 : ClF5 , BrF5 , IF5
4) XY7 : IF7

4. VARIOUS TYPES OF INTERHALOGEN
COMPOUNDS
ELEMENT FLUORIDE CHLORIDE BROMIDE IODIDE
FLUORINE - - - -
CHLORINE ClF , ClF3 , ClF5 - - -
BROMINE BrF , BrF3 , BrF5 BrCl - -
IODINE IF , IF3 , IF5 , IF7 ICl , ICl3 IBr -

5. PREPARATION OF INTERHALOGEN
COMPOUNDS
i) Halogen molecules react directly to form interhalogen compounds.
Ex: Equal volume of chlorine and fluorine combine at 473K to form
chlorine monofluoride.
ii) A halogen molecule reacts with lower interhalogen to form a new
interhalogen compound.
Ex: Fluorine reacts with iodine pentafluoride at 543K to form iodine
heptafluoride.

6. SOME PROPERTIES OF INTERHALOGEN
COMPOUNDS
• PHYSICAL STATE : These molecules are covalent in nature.
• COLOUR : These compounds are colourless.
• BOILING POINT : Boiling point increases with increase with
electronegativity difference.
• THERMAL STABILITY: Thermal stability decreases with decrease in
electronegativity difference.
• REACTIVITY : AB type of compounds are more reactive than A2 and B2
molecules.

7. INTERHALOGEN COMPOUNDS OF XY TYPE
Eg : Iodine monobromide (IBr)
PREPARATION : It is obtained by the direct combination of elements.
PROPERTIES :
 It is hard, crystalline solid of grey violet colour.
 Its vapour dissociate to a small extent on heating.
 IBr is an electrical conductor when in molten state.

8. INTERHALOGEN COMPOUNDS OF XY3 TYPE
Eg : Chlorine trifluoride (ClF3)
PREPARATION : It is prepared by the action of Cl2 on F2 at 200-300◦C in a Cu vessel.
PROPERTIES:
 It is a colourless gas which condenses to give a pale green liquid.
 Hydrolysis: It is hydrolysed by H20 forming ClOF.
 Action of F2 and Br2:
i) When ClF3 reacts with F2 , it gets fluorinated with F2 , forming the higher
interhalogens ClF5.
ii) When ClF3 reacts with Br2 at 10 ◦C, BrF3 is obtained. Bent T Shape

9. INTERHALOGEN COMPOUNDS OF XY5 TYPE
Eg : Iodine pentafluoride (IF5)
PREPARATION: It is prepared by the direct combination of I2
and F2 (excess).
PROPERTIES:
 It is a colourless liquid whose melting point is 9.6 ◦C.
 Good conductor of electricity.
Hydrolysis: It is hydrolysed by water to give halogen acid and oxy-acid of
larger halogen atom.

10. INTERHALOGEN COMPOUNDS OF XY7 TYPE
Eg : Iodine heptafluoride (IF7)
PREPARATION: It is prepared by the action of F2 on IF5 at 250◦C -300◦C.
PROPERTIES:
 It is gas at ordinary temperature.
 Highly reactive
 Hydrolysis: It is hydrolysed by water giving HF and H5IO6.

11. USES OF INTERHALOGEN
COMPOUNDS
• Used as non-water solvents.
• Used as a catalyst.
• Used as fluorinating compounds.

12. PSEUDOHALOGENS
• Pseudohalogens are groups formed by the combination of two or
more p block elements with a unit negative charge.
Eg: Cyanogen (CN)2 , Thiocyanogen (SCN)2 etc.

13. PROPERTIES OF PSEUDOHALOGENS
 These are volatile.
 Pseudohalogens, like the halogens, add at ethylenic double bond
linkage.
 Pseudohalogens , like the halogens, react with alkalies.
 Pseudohalogens form covalent pseudohalides.

14. • Eg : Thiocyanogen (SCN)2
PREPARATION: It is prepared by Pb(SCN)2 with Br2 in the real solution
at 0 ◦C.
PROPERTIES:
 It is yellow solid
 Insoluble in water.
 It oxidises Cu(I) salts to Cu(II) salts.
 Sulphur is precipitated from H2S.

15. USES OF PSEUDOHALOGEN
COMPOUNDS
• Used as an oxidising agent.
• Used for the determination of unsaturation in organic
compound.

16. REFERENCES
• ADVANCED INORGANIC CHEMISTRY BY
SATYAPRAKASH.
• SELECTED TOPICS IN INORGANIC CHEMISTRY BY
S CHAND.