Interhalogens and Pseudohalogens

Interhalogens and Pseudohalogens

1. INTERHALOGENS AND PSEUDOHALOGENS

2. INTERHALOGEN COMPOUNDS When two different halogens react with each other, interhalogen compounds are formed. In general, XY n 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 : XY : ClF , BrF , BrCl , ICl , IBr XY 3 : ClF 3 , BrF 3 , IF 3 , ICl 3 XY 5 : ClF 5 , BrF 5 , IF 5 XY 7 : IF 7

4. VARIOUS TYPES OF INTERHALOGEN COMPOUNDS ELEMENT FLUORIDE CHLORIDE BROMIDE IODIDE FLUORINE - - - - CHLORINE ClF , ClF 3 , ClF 5 - - - BROMINE BrF , BrF 3 , BrF 5 BrCl - - IODINE IF , IF 3 , IF 5 , IF 7 ICl , ICl 3 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 A 2 and B 2 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 XY 3 TYPE Eg : Chlorine trifluoride (ClF 3 ) PREPARATION : It is prepared by the action of Cl 2 on F 2 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 H 2 0 forming ClOF. Action of F 2 and Br 2 : i) When ClF 3 reacts with F 2 , it gets fluorinated with F 2 , forming the higher interhalogens ClF 5 . ii) When ClF3 reacts with Br 2 at 10 ◦ C , BrF 3 is obtained. Bent T Shape

9. INTERHALOGEN COMPOUNDS OF XY 5 TYPE Eg : Iodine pentafluoride (IF 5 ) PREPARATION : It is prepared by the direct combination of I 2 and F 2 (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 XY 7 TYPE Eg : Iodine heptafluoride (IF 7 ) PREPARATION : It is prepared by the action of F 2 on IF 5 at 250 ◦ C -300 ◦ C. PROPERTIES : It is gas at ordinary temperature. Highly reactive Hydrolysis: It is hydrolysed by water giving HF and H 5 IO 6 .

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 Br 2 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 H 2 S.

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.