2. New Way Chemistry for Hong Kong A-Level Book 11 Chapter 9 Intermediate Type of Bonding 9.1Incomplete Electron Transfer in Ionic Compounds Ionic Compounds 9.2Electronegativity of Elements 9.3Polarity of Covalent Bonds

3. New Way Chemistry for Hong Kong A-Level Book 12 Born-Haber Cycle for the formation of sodium chloride  H lattice  can be found from the Born-Haber Cycle Expt al value of  H lattice  9.1 Incomplete Electron Transfer in Ionic Compounds (SB p.234) Theoretical Values of Lattice Enthalpy

4. New Way Chemistry for Hong Kong A-Level Book 13 Another way of getting the value of  H lattice  Assuming perfect ionic model 1. Ions are perfect spheres with uniform charge distribution. 2. The cations and anions are in contact with each other and with electrostatic interactions in between. 9.1 Incomplete Electron Transfer in Ionic Compounds (SB p.234)

5. New Way Chemistry for Hong Kong A-Level Book 14 Another way of getting the value of  H lattice  The force(F) between two point charges q 1 and q 2 separated by a distance R is given by: R _ q2q2 q1q1 +  H lattice  = work done when the ions are allowed to be brought from infinite separation to the internuclear distance in the ionic lattice where r is the normal internuclear distance Theoretical value of  H lattice  9.1 Incomplete Electron Transfer in Ionic Compounds (SB p.234)

6. New Way Chemistry for Hong Kong A-Level Book 15 Increasing polarization of a negative ion by a positive ion Polarization / Distortion of electron cloud = Covalent character in ionic bond 9.1 Incomplete Electron Transfer in Ionic Compounds (SB p.236) Polarizing power of cation polarizability of anion

7. New Way Chemistry for Hong Kong A-Level Book 16 Polarizing power of a cation increases as its charge density (charge/volume ratio) increases.  polarizing power: Al 3+ > Mg 2+ > Na + and Li + > Na + > K + 9.1 Incomplete Electron Transfer in Ionic Compounds (SB p.236) Increasing polarization of a negative ion by a positive ion Polarizing power of cation

8. New Way Chemistry for Hong Kong A-Level Book 17 Polarizability of a anion increases as its size increases.  polarizability: I - > Br - > Cl - and S 2- > O 2- Increasing polarization of a negative ion by a positive ion 9.1 Incomplete Electron Transfer in Ionic Compounds (SB p.236) polarizability of anion

9. New Way Chemistry for Hong Kong A-Level Book 18 Electronegativity is defined as the relative tendency of an atom to attract a bonding pair of electrons towards itself. XYXY X : Y 9.2 Electronegativity of Elements (SB p.238) Electronegativity values of some representative elements

10. New Way Chemistry for Hong Kong A-Level Book 19 Bond Polarization 9.3 Polarity of Covalent Bonds (SB p.239) a pure covalent bond a polar covalent bond

11. New Way Chemistry for Hong Kong A-Level Book 110 Relationship between the type of bond and difference in electronegativity between two bonded atoms BondDifference in electronegativity between the two bonded atoms Type of bond Cl-Cl Cl-C Cl-H F-Li 3.0 - 3.0 = 0 3.0 - 2.5 = 0.5 3.0 - 2.1 = 0.9 4.0 - 1.0 = 3.0 Covalent Polar covalent Ionic 9.3 Polarity of Covalent Bonds (SB p.239)

12. New Way Chemistry for Hong Kong A-Level Book 111 Relationship between bond nature and difference in electronegativity between bonded atoms. 9.3 Polarity of Covalent Bonds (SB p.240)

13. New Way Chemistry for Hong Kong A-Level Book 112 Polarity of Molecules  (Debye, D) = q x d 9.3 Polarity of Covalent Bonds (SB p.240) How polar is the molecule? represented by dipole moment (  )

14. New Way Chemistry for Hong Kong A-Level Book 113 9.3 Polarity of Covalent Bonds (SB p.241) The effect of an electric field on polar molecules

15. New Way Chemistry for Hong Kong A-Level Book 114 The effect of an electric field on non-polar molecules 9.3 Polarity of Covalent Bonds (SB p.241)

16. New Way Chemistry for Hong Kong A-Level Book 115 Non-polar Molecules 9.3 Polarity of Covalent Bonds (SB p.242) ShapeMoleculeCancelling out of dipole moments Linear Trigonal planar Tetrahedral

17. New Way Chemistry for Hong Kong A-Level Book 116 9.3 Polarity of Covalent Bonds (SB p.242) Non-polar Molecules (Cont’d) ShapeMoleculeCancelling out of dipole moments Trigonal bipyramidal Octaherdral

18. New Way Chemistry for Hong Kong A-Level Book 117 Polar Molecules 9.3 Polarity of Covalent Bonds (SB p.243) ShapeMoleculeDipole moment of individual polar bonds Net resultant dipole moment V-shaped ( or bent) Trigonal pyramidal Tetrahedral

19. New Way Chemistry for Hong Kong A-Level Book 118 Use of Dipole Moments 9.3 Polarity of Covalent Bonds (SB p.243)

20. New Way Chemistry for Hong Kong A-Level Book 119 Effect of a Non-uniform Electric Field on polar and Non-polar Liquid 9.3 Polarity of Covalent Bonds (SB p.244) Solvents showing a marked deflection Solvents showing no deflection Trichloromethane, CHCl 3 Ethanol, CH 3 CH 2 OH Propanone Water, H 2 O Tetrachloromethane, CCl 4 Cyclohexane Benzene

21. New Way Chemistry for Hong Kong A-Level Book 120 The END