Bonding
What exactly is a bond? Depends…Ionic or Covalent? Polar?
NON-POLAR COVALENT=> equal sharing of electron pair
0 < ∆EN < 0.4
POLAR COVALENT= unequal sharing of electron pairs, e-’s
spend more time closer to one atom, 0.4 < ∆EN < 1.7
IONIC “BOND”= transfer of electrons, no physical
connection to one another, atoms are held together by
an electrostatic attraction, ∆EN > 1.7
Molecular Polarity
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Tutorial 1: p. 226
Figure 6: p. 228
p. 227 #1,2
HW: p. 229 #1-7ab
No molecular dipole
=> non-polar molecule
Molecular Dipole is present
=>
molecule
No polar
molecular
dipole
=> non-polar molecule
Molecular Dipole is present
=> polar molecule
Which process requires more energy?
Why?
H2O(l)  H2O(g)
or
2 H2O(l)  2 H2(g) + O2(g)
Intermolecular Forces
London force (dispersion)
•due to electrostatic
attraction b/w protons in one
molecule and electrons of
neighbouring molecules
•strength α # of eCl2 bp = -35°C
Cl2 has 34 e-. I2 has 106 e-.
I2
bp = 84°C
I2 has more e- => greater LDF =>
Explain the trend in bp. higher bp
Intermolecular Forces
dipole-dipole force
•due to attraction of one
dipole by surrounding dipoles
•strength α molecular
polarity
CH2O
bp = -21°C
C2H6
bp = -89°C
Explain the trend in bp.
Include diagrams to support
your explanation.
CH2O is a polar molecule => has
a dipole force, LDF (16 e-)
C2H6 is a non-polar molecule =>
no dipole force, only LDF (18 e-)
CH2O has higher bp due to
dipole-dipole force
Predict which substance has the stronger
dipole force: HCl or HBr
HCl is the more polar molecule (ΔEN is greater) =>
stronger dipole forces
(Draw diagrams to support your explanation.)
Intermolecular Forces
Hydrogen bonding
•due to attraction of a H
bonded to a highly EN atom
(O, N or F) in one molecule by
the lone pair of e- on a highly
electronegative atom of a
neighbouring molecule
H2Te
bp = -10°C
H2Se
bp = -50°C
H2S
bp = -80°C
H2O
bp = 100°C
Explain the trend in bp.
Intermolecular Forces
Identify the
type of IMF
Strongest?
Properties of Liquids
Cohesive forces:
• attractions b/w like
molecules
Adhesive forces:
• attractions b/w unlike
molecules
Capillary Action
• Water is transported
in thin tubes from
roots to shoots.
• adhesive forces (b/w
H2O and sides of
tubes) and cohesive
forces (b/w H2O
molecules)
• Water is pulled up
against gravity!
Intermolecular Forces and Properties
i) Boiling and melting pt
ii) Surface tension
iii) Meniscus shape
iv) Capillary action
v) Volatility
vi) Viscosity
vii) Solubility
viii) Wetting Action
ix) Hydrophobicity
Why is glycerol more viscous than
water?
Homework
• Section 4.7
• p. 244 #1,2
• p. 247 #1-6