Bonding Bonding Intermolecular forces

SAROJ MANOJ RAMAN, OCC

Kinds of moleculesKinds of molecules

Proof for existence of Proof for existence of intermolecular forcesintermolecular forces

Types of Intermolecular Types of Intermolecular forcesforces

Examples to explain Van der waals’ Examples to explain Van der waals’ forcesforces

Examples to explain dipole-dipole Examples to explain dipole-dipole forces forces

Hydrogen bondingHydrogen bondingHδ+— Fδ- ---------------Hδ+— Fδ-

hydrogen bondConsiderably stronger than other

intermolecular forces.Affects the physical properties of

the compounds in which it exists.

Examples of H-BondingExamples of H-Bonding

Hydrogen Bonding in diff. Hydrogen Bonding in diff. compoundscompounds

Examples of H-Bonding Examples of H-Bonding contd….contd….

Examples of H-Bonding Examples of H-Bonding contd….contd….

Trends in Boiling points of Trends in Boiling points of Groups 4,5,6 and 7Groups 4,5,6 and 7

Examples of H-Bonding Examples of H-Bonding contd….contd….

Anomalous behavior of Anomalous behavior of WaterWater

Structure of ICEStructure of ICE

Hydrogen Bonds in Water, Hydrogen Bonds in Water, IceIce

Compare HCompare H22O and HO and H22SSProperties Water Hydrogen

sulphide

Molar enthalpy of fusion 6.0 kJmol-1 2.4 kJmol-1

Molar enthalpy of vaporization

41.0 kJmol-1 19.0 kJmol-1

State at room temperature & Pressure

Liquid Gas

Electro negativity Very high Less

Size O atom is small

S is larger than O

Hydrogen Bonding 2 H bonds per molecule of water

No H Bonding

Effect of H bonding on Effect of H bonding on Organic compounds- case 1Organic compounds- case 1

Dimer of Ethanoic acidDimer of Ethanoic acid

Effect of H bonding on Effect of H bonding on Organic compounds- case 2Organic compounds- case 2Propanone is miscible in water

but it has no H bonding between propanone molecules

This is because its O atoms can bond to water molecules.

Effect of H bonding on Effect of H bonding on Organic compounds- case 3Organic compounds- case 3p- nitro phenol or 4- nitro phenol

is having intermolecular H bonds , stronger forces of interaction between molecules and so its BP is 279°C

o- nitro phenol or 2- nitro phenol has intramolecular H bonds, weaker forces of interaction between molecules and so has lower BP of 216°C

Biological importance of H Biological importance of H bondingbondingDNA pairing occurs due to H

bonds.Secondary structure of proteins

(α helix and β pleated proteins) α helix-is an example of INTRA

MOLECULAR H Bonding

Hydrogen bonds in DNA Base Hydrogen bonds in DNA Base PairsPairs2 H bonds between Adenine and Thymine3 H bonds between Cytosine and Guanine