Chemistry 11 (HL)
Unit 4 / IB Topic 4.3
Chemical Bonding 8
Intermolecular Forces in Covalent Substances – Practice Problems
SUMMARY
Make a summary of intermolecular forces:
type of IMF
relative strength
What is needed
for this type of
IMF to form?
What type of
covalent
molecules form
these IMFs?
3 examples of
substances with
this IMF
1.
Identify the major type of intermolecular force between the molecules of each substance:
substance
a)
SO3
b)
PCl3
c)
HF
d)
H 2S
Lewis structure
bond ∆EN +
bond type
all S-O
bonds:
∆EN = 0.8
polar cov.
bond
all P-Cl
bonds:
∆EN = 1.0
polar cov.
bond
∆EN = 1.8
very polar
cov. bond
All H-S
bonds:
∆EN = 0.4
weakly
polar cov.
bonds
shape
molecular
polarity
trigonal
planar
non-polar
molecule
trigonal
pyramidal
polar
molecule
type of
intermolecular force
between molecules
of this substance
(linear)
bent /
anglular
p. 1
Chemistry 11 (HL)
e)
HCl
Unit 4 / IB Topic 4.3
∆EN = 1.0
polar cov
bond
C-H
bonds:
∆EN = 0.4
weakly
polar cov.
f)
CH3OH
C-O
bond:
∆EN = 0.8
polar cov.
O-H
bond:
∆EN = 1.2
Polar cov.
g)
SO2
h)
CF4
i)
NH3
j)
H2CO
k)
CO2
l)
SF4
p. 2
Chemistry 11 (HL)
2.
3.
Unit 4 / IB Topic 4.3
Which substance in each pair would have stronger intermolecular forces of attraction?
Why?
a)
chlorine or bromine
b)
hydrogen fluoride or hydrogen chloride
c)
methane (CH4) or carbon tetrafluoride (CF4)
d)
ammonia (NH3) or phosphorus trihydride (PH3)
e)
hydrogen chloride or hydrogen iodide
a)
During physical changes like melting and boiling (or evaporation), energy is
needed to break the intermolecular forces.
The substance in the box below represents a liquid. Draw what the substance
looks like in the gas phase.
liquid
gas
b)
When the strength of the intermolecular forces increases, what happens to
melting point or boiling point?
c)
Which substance in each part in Q2 would have a higher boiling point?
Cl2 vs Br2
HF vs HCl
NH3 vs PH3
HCl vs HI
CH4 vs CF4
p. 3
Chemistry 11 (HL)
4.
Unit 4 / IB Topic 4.3
Rank each set of substances in order of increasing boiling point. Justify your answer.
a)
O2
N2
CO2
b)
These substances all have similar molar masses and number of electrons.
C3H7OH
5.
C4H10
SO2
Which of the following substances would have hydrogen bonding?
NH3
6.
H2
COCl2
PH3
CH3OH
CH3F
H2CO
CH3COOH
This graph shows the boiling points of the Group 16 hydrides:
http://alevelchem.com/aqa_a_level_chemistry/unit3.1/sub313/03.htm
a)
Describe the trend.
b)
Explain the differences in the boiling points.
p. 4