Ch 4 Chemistry Class 11 Notes

• Definition of Intermolecular Forces and Types of Intermolecular Forces
• Define and explain Instantaneous dipole-induced dipole forces or London Dispersion Forces 
• Define and explain Hydrogen Bonding 
• Electronegative atoms creating hydrogen bonding
• Properties and Application of Compounds containing Hydrogen Bonding
• Hydrogen Bonding in Carbohydrates
• Define Manometric Method
• Classification of Solids
• Define Ionic Solids with its examples
• Define Covalent Solids and Types of covalent solids
• Define Molecular Solids and Types of intermolecular forces
• Structure of iodine
• Define and explain Metallic Solids 
• State Valence Bond Theory
• State Molecular Orbital Theory
• Properties of metallic solids
• Important long questions from past papers
• Instantaneous Dipole Induced Dipole Forces or London Dispersion Forces: Definition The momentary force of attraction created between instantaneous dipole and the induced dipole is called instantaneous dipole-induced dipole interaction or London force. Explanation A German physicist Fritz London in 1930 offered a simple explanation for these weak attractive forces between non-polar molecules. Attractive forces among He atoms 1) Generation of instantaneous dipole • In helium gas, the electrons of one atom influence the moving electrons of the other atom. • Electrons repel each other and they tend to stay as far apart as possible. • When the electrons of one atom come close to the electron of other atom, they are pushed away from each other. • In this way, a temporary dipole is created in the atom. • At any moment the electron density of the atom is no more symmetrical. • It has more negative charge on one side than on the other. • At that particular instant, the helium atom becomes a dipole. • This is called instantaneous dipole. 2) Generation of induced dipole • The instantaneous dipole then disturbs the electronic cloud of the other nearby atom. • A dipole is induced in the second atom. • This is called induced dipole. Characteristics • It is a very short-lived attraction because the electrons keep moving. • London forces are present in all types of molecules whether polar or non-polar, but they are very’ significant for non-polar molecules like Cl2, H2 and noble gases.
• Hydrogen Bonding in Carbohydrates: The food materials like carbohydrates include glucose, fructose and sucrose. They all have -OH groups in them which are responsible for hydrogen bonding in them. 6. Hydrogen Bonding in Paints, Dyes and Textile Materials H-bonding in paints and dyes The adhesive action of paints and dyes is due to hydrogen bonding. H-bonding in glue and honey Hydrogen bonding makes glue and honey as sticky substances. H-bonding in cotton, silk or synthetic fibres Hydrogen bonding is of vital importance in the thread making materials. This hydrogen bonding is responsible for their rigidity and tensile strength. 
• Determination of Vapour Pressure. Difference in the heights of the columns of Hg in liquid determines the vapour pressure of the liquid. 8. The column of mercury in the manometer facing the vapours of the liquid is depressed. 9. The other column which faces the atmospheric pressure rises. 10. The pressure on the surface of the liquid in the flask is equal to the sum of the atmospheric pressure and the vapour pressure of liquid. 11. The column of manometer facing the liquid is more depressed than facing the atmosphere.