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

New Way Chemistry for Hong Kong A-Level Book 11

Chapter 9Chapter 9Intermediate Type of BondingIntermediate Type of Bonding

9.19.1 Incomplete Electron Transfer inIncomplete Electron Transfer in

Ionic CompoundsIonic Compounds

9.29.2 Electronegativity of ElementsElectronegativity of Elements

9.39.3 Polarity of Covalent BondsPolarity of Covalent Bonds


Born-Haber Cycle for the formation of sodium chloride

Hlattice can be fo

und from the Born-Haber Cycle

Exptal value of Hlattice

9.1 Incomplete Electron Transfer in Ionic Compounds (SB p.234)

Theoretical Values of Lattice Enthalpy


Another way of getting the value of Hlattice

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.



Another way of getting the value of Hlattice

R

qqk F 21

The force(F) between two point charges q1 and q2 separated by a distance R is given by:

R _

q2q1

+

Hlattice = work done when the ions are allowed to be brought from i

nfinite separation to the internuclear distance in the ionic lattice

dR R

qqk H

r21

lattice

where r is the normal internuclear distance

Theoretical value of H

lattice



Increasing polarization of a negative ion by a positive ion

Polarization / Distortion of electron cloud

Polarization / Distortion of electron cloud=Covalent character in ionic bond

Covalent character in ionic bond


Polarizing power of cation

polarizability of anion


Polarizing power of a cationincreases as its charge density(charge/volume ratio) increases.

polarizing power:Al3+ > Mg2+ > Na+ andLi+ > Na+ > K+



Polarizing power of cation


Polarizability of a anionincreases as its size increases.

polarizability:I- > Br- > Cl- andS2- > O2-



polarizability of anion


Electronegativity is defined as the relative tendency of an atom to attract a bonding pair of electrons towards itself.

Electronegativity is defined as the relative tendency of an atom to attract a bonding pair of electrons towards itself.

XY

X : Y

9.2 Electronegativity of Elements (SB p.238)

Electronegativity values of some representative elements


Bond Polarization

9.3 Polarity of Covalent Bonds (SB p.239)

a pure covalent bonda polar covalent bond


Relationship between the type of bond and difference in electronegativity between two bonded atoms

Bond Difference 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

Polar covalent

Ionic



Relationship between bond nature and difference in electronegativity between bonded atoms.



Polarity of Molecules

(Debye, D) = q x d (Debye, D) = q x d


How polar is the molecule?How polar is the molecule?

represented by dipole moment ()



The effect of an electric field on polar molecules


The effect of an electric field on non-polar molecules9.3 Polarity of Covalent Bonds (SB p.241)


Non-polar Molecules9.3 Polarity of Covalent Bonds (SB p.242)

Shape Molecule Cancelling out of dipole moments

Linear

Trigonal planar

Tetrahedral



Non-polar Molecules (Cont’d)

Shape Molecule Cancelling out of dipole moments

Trigonal bipyramidal

Octaherdral


Polar Molecules9.3 Polarity of Covalent Bonds (SB p.243)

Shape Molecule Dipole moment of individual polar bonds

Net resultant dipole moment

V-shaped

( or bent)

Trigonal pyramidal

Tetrahedral


Use of Dipole Moments



Effect of a Non-uniform Electric Field on polar and Non-polar Liquid


Solvents showing a marked deflection

Solvents showing no deflection

Trichloromethane, CHCl3

Ethanol,

CH3CH2OH

Propanone

Water, H2O

Tetrachloromethane,

CCl4

Cyclohexane

Benzene


The END

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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