The document discusses different types of intermolecular forces including London dispersion forces, dipole-dipole forces, dipole-induced dipole forces, ion-dipole interactions, and hydrogen bonding. It provides examples of how these forces influence the properties of substances such as their melting and boiling points. Hydrogen bonding specifically is described as being an important intermolecular force that influences the properties of water, alcohols, and other polar molecules.

1. Intermolecular FORCESPRESENTED BY PRATIBHA KOHLIDEPARTMENT OF CHEMISTRY, DELHI PUBLIC SCHOOL, RK PURAM

2. Why do some solids dissolve in water but others do not?

3. What happens when noble gases liquefy?

4. Why are some substances gases at room temperature, but others are liquid or solid? The answers lie in………Intermolecular Forces

5. Intermolecular forces may be attractive or repulsive.Johannes D van der Waals, Dutch, was the first to postulate intermolecular forces in developing a theory to account for properties of real gases.

6. van der Waals forces includeLondon forces

7. Dipole - dipole forces

8. Dipole - induced dipole forcesOther intermolecular forces are Ion - dipole interactions

9. Ion - induced dipole interactions

10. Hydrogen BondingLondon Forces (Dispersion Forces)These arise from temporary variations in electron density in atoms and molecules. At any instant , the electron distribution may be unsymmetrical and hence produce an instantaneous dipole. This can cause an induced transient dipole in the neighbouring molecule and cause the molecules to be attracted.

11. London forces

12. Dispersion forces are present between all molecules , whether polar or non-polar.Dispersion forces are stronger in molecules that are easily polarizable.Larger and heavier molecules exhibit stronger dispersion forces than smaller and lighter ones.

13. Shapes of molecules affect magnitude of dispersion forces The cylindrical shape of n-pentane has greater surface area .Hence, n-pentane has greater London forces .The spherical shape of neo-pentane has lesser surface area. So, it has lesser London attractive forces.

14. Dipole-dipole forces(Keesom Forces)These forces arise due to interaction between oppositely charged ends of polar molecules. Greater the dipole moment of molecules , greater are the forces of attraction.

15. DIPOLE-DIPOLE FORCES

16. Dipole-induced dipole forcesThese operate between polar molecules having permanent dipole and the molecules having no permanent dipole.The polar molecule induces a dipole in the neighbouring non-polar molecule.The interaction energy depends onDipole moment of polar molecule

17. Polarisability of nonpolar molecule Oxygen gas can dissolve in water because the permanent dipole in water can induce a dipole in oxygen molecules.

18. Non-polar iodine dissolves in polar ethanol due to dipole-induced dipole forces.Ion –dipole InteractionsThese interactions depend on Charge and size of ion

19. Magnitude of dipole moment of polar molecule

20. Size of polar moleculeHydrationOf Sodium ions

21. Hydration of Chloride Ions

22. Hydrogen BONDINGIt is an electrostatic force of attraction that exists between covalently bonded hydrogen atom of one molecule and the electronegative atom of another molecule.

23. It is represented by a dotted line - - - .Conditions for Hydrogen Bond formationA hydrogen atom attached to a relatively electronegative atom is a hydrogen bond donor. This electronegative atom is usually fluorine, oxygen, or nitrogen. An electronegative atom such as fluorine, oxygen, or nitrogen is a hydrogen bond acceptor, regardless of whether it is bonded to a hydrogen atom or not.

24. INTERMOLECULAR HYDROGEN BONDIt is formed between two different molecules of the same or different substances, eg.

25. Hydrogen bond between molecules of ammonia

26. Hydrogen bond between molecules of water and alcoholINTRAMOLECULARHYDROGEN BONDIt is formed between the hydrogen atom and a highly electronegative atom present in different bonds within the same molecule, eg.

27. o-salicylaldehyde

28. o- nitrobenzoic acidAssociation of water molecules

29. HYDROGEN FLUORIDE In the solid state , hydrogen fluoride consists of long zig-zag chains of molecules associated together by hydrogen bonding. Hence, hydrogen fluoride molecule can also be represented as (HF)n. However, in gaseous or liquid state , the chain becomes linear.

30. Alcohols have high miscibility in water due to formation of intermolecular hydrogen bonds between water and alcohol molecules.

31. Higher melting and boiling pointsDramatically higher boiling points of NH3, H2O, and HF compared to the heavier analogues PH3, H2S, and HCl.