Chapter 3: Molecular Compounds and Intermolecular Forces
Section 3.1: Molecular Compounds, pages 35–36
1. Major sources for molecular compounds include living things and fossil fuels.
2. True
3. Table 1 Renewable and Non-Renewable Resources
Renewable or nonResource
Explanation
renewable?
newspaper
renewable
coal
non-renewable
plastic wrap
non-renewable
blueberries
renewable
4. c
5. Table 2 Properties of Materials
Material
Reusable
cotton
X
steel
leftover pizza
plastic cellphone case
pop bottle
X
aluminum foil
X
leather shoe
X
Newspaper is made of wood. New trees from which
to make more paper can be grown.
When coal is used, it gets broken down by chemical
reactions into things that cannot be recycled.
Plastic is a petrochemical that was created from a
fossil fuel. Fossil fuels take millions of years to form
and cannot be replenished from discarded plastic
wrap (or any other fossil-fuel breakdown product)
any time soon.
Blueberries are a fruit that grows. Once used up,
more blueberries can be grown to replace the amount
that was used.
Recyclable
X
Biodegradable
Compostable
Upcyclable
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
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6. Figure 1
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Section 3.2: Explore an Issue in Molecular Compounds: DEET in Insect
Repellents, page 37
1. The purpose of an insect repellent is to ward off insects while the purpose of an insecticide is to kill insects.
2. Fabrics in which DEET is soluble are likely to be damaged by DEET.
3. d
4. Answers may vary. Sample answer:
Table 1 Issues and Ranking for Insect Repellents Featured in a Store
Issue
Rank Reason
the concentration of
5
This is fairly important because doctors recommend keeping the
insect repellent
concentration of chemicals like DEET low for children.
the active ingredient in
3
This is extremely important because the active ingredient determines
the insect repellent
how safe and effective the product is.
the price of insect
6
This is somewhat important because I will not buy the product if it is
repellent
too expensive.
how effective the
1
This is the most important issue for me. If the product is effective, then
product is
I will feel good about recommending it to customers.
reported health concerns
4
This is very important. If there are health problems with a given
about the product
product, I will not use it.
how well known the
7
This is not that important. Any company is acceptable as long as its
company is
product is safe and effective.
how safe the product is
2
This is extremely important. I will not use a product that is not safe for
for children
children.
5. Answers may vary. Sample answer:: I would choose a well-known brand of insect repellent that features
DEET in a 10 % concentration. Any greater concentration and I think I may be at risk.
Section 3.3: Polar Bonds and Polar Molecules, pages 38–40
1. In a diatomic molecule with a polar covalent bond, the electrons tend to cluster more closely to the atom that
is more electronegative.
2. True
3. b
4. (a) !EN C–Cl = 3.2 – 2.6
= 0.6
!EN C–C = 2.6 – 2.6
!EN C–H
=0
= 2.6 – 2.2
= 0.4
(b) C–Cl is the most polar. C–H is slightly polar. C–C is non-polar.
(c)
Copyright © 2011 Nelson Education Ltd. Chapter 3: Molecular Compounds and Intermolecular Forces 3-3
5. Polarity of HCl:
Two atoms make up HCl, one hydrogen and one chlorine.
Lewis structure:
The molecule has one covalent bond.
!EN Cl–H = 3.2 – 2.2
= 1.0
This is polar covalent.
Partial charges:
With only one polar covalent bond, the molecule is polar no matter what; therefore, HCl is a polar molecule.
6. Polarity of H2:
Two hydrogen atoms make up H2.
Lewis structure:
The molecule has one covalent bond.
ΔEN = 0. This is non-polar covalent.
With no polar covalent bonds, the H2 molecule is non-polar.
7. Polarity of NF3:
Four atoms make up NF3, three fluorines and one nitrogen.
Lewis structure:
There are three covalent bonds.
!EN F–N = 4.0 – 3.0
= 1.0
This is polar covalent.
Partial charges:
With only one polar covalent bond, the molecule would be polar no matter what. With multiple polar covalent
bonds, the molecule may or may not be polar. But the molecule is asymmetrical, so it is a polar molecule.
8. Polarity of CO2:
Three atoms make up CO2, two oxygens and one nitrogen.
Lewis structure:
There are four covalent bonds.
!EN O–C = 3.4 – 2.6
= 0.8
This is polar covalent.
But CO2 is a symmetrical, linear molecule, with a symmetrical placement of the two oxygen atoms on either
side of the carbon, The two polar covalent bonds cancel out each other, making CO2 a non-polar molecule.
Copyright © 2011 Nelson Education Ltd. Chapter 3: Molecular Compounds and Intermolecular Forces 3-4
9. Polarity of NO2:
Three atoms make up NO2, two oxygens and one nitrogen.
Lewis structure:
There are three covalent bonds.
!EN O–N = 3.4 – 3.0
= 0.4
This is polar covalent.
Partial charges:
Since the NO2 molecule is lopsided, or bent, we can consider that it has two ends: a negatively charged oxygen
end and a positively charged nitrogen end. Thus, the NO2 molecule is polar.
Section 3.4: Intermolecular Forces, pages 41–42
1. Ionic compounds are held together by the ionic bonds of the elements that make up the compound, not by
intermolecular forces.
2. False. A hydrogen bond is a special form of the dipole–dipole force.
3. d
4. The melting point of a molecular compound depends primarily on how tightly its molecules are held
together by the three van der Waals forces.
5. Table 1 Properties of Elements
Rank Type of force or bond Causes
Example
1
ionic bond
electrostatic force between
crystalline structure of NaCl
ions
2
hydrogen bond
highly polar nature of small
water surface tension
molecules
3
dipole–dipole force
polar attraction between
hydrogen being attracted to nearby
parts of molecules
chlorine in HCl
4
London dispersion
temporary gaps in electron
attraction of bromine to itself in Br2
force
clouds
6. (a) Ball and stick models for HCl and H2O:
(b) A dipole–dipole force will arise between H and Cl in a group of HCl molecules.
(c) Model of a group of HCl molecules and the intermolecular forces between them:
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(d) A model of a group of water molecules and the intermolecular forces between them:
7. (a) The electronegativity difference between the two atoms in the iodine molecule is zero.
(b) I2 is a non-polar molecule.
(c) The explanation for why the melting and boiling points of I2 (113.7 °C and 184.3 °C) are higher than those
of water, a highly polar molecule, is as follows: Iodine atoms are large—each iodine atom has 53 protons and
53 electrons. This high number of protons and electrons gives iodine atoms ample opportunity to experience
London dispersion forces, which create attraction between molecules and hold the molecules together as a
solid at standard temperatures.
Section 3.5: Hydrogen Bonding and Water, pages 43–44
1. True
2. b
3. On a planet with an average daily temperature range of between –100 °C and –50 °C, you would expect to
find
(a) (i) Ammonia would be in a solid state or liquid state.
(ii) Hydrogen sulfide would be in a solid state, liquid state, or gas state.
(iii) Water would be in a solid state only.
(b) Life as we know it operates on a planet in which a common compound exists in all three states. Therefore,
of water, ammonia, and hydrogen sulfide, hydrogen sulfide would be more likely to support life on this planet.
4. (a) The water temperature in the lake might rise a degree or so, if at all.
(b) Water is slow to heat up when temperatures rise. Then, when temperatures drop, water is slow to cool
down.
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5. Figure 1
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Section 3.6: Green Chemistry in Action: Choosing the Right Materials, pages 45–
46
1. True
2. Figure 1
3. (a) ii, iii; (b) i, ii
4. b
5. Table 1 Conventional vs. Green Products
Conventional product
Step
requirement
raw materials renewable or nonrenewable
production
efficient
process
product
efficient
function
by-products
not an issue
Green product requirement
renewable only
Advantage of green product
does not deplete natural
resources
efficient, every step
ensures no damage to
environmentally safe
environment
efficient without
ensures no damage to
environmental damage
environment
no environmental damage
ensures no damage to
environment
end-ofnot an issue
must have environmentally
ensures no damage to
product life
friendly disposal
environment
6. (3) Increased kinetic energy can overwhelm intermolecular forces between molecules in a plastic. (4) This
can melt, deform, or decompose plastic computer cases. (6) Since they do not break down easily, BFRs cause
environmental problems. (1) Computers can generate a great deal of thermal energy. (7) As an alternative to
BFRs, scientists are developing bioplastics that can withstand high temperatures yet can be biodegraded.
(5) To prevent damage, chemists use BFR plastics for computer cases that can withstand high temperatures.
(2) Thermal energy increases kinetic energy in solid materials.
7. Answers may vary. Sample answer: I think imposing a disposal cost for disposable diapers when they are
purchased would be fair. Right now, parents dispose of millions of diapers that just sit in landfills. Imposing a
cost could provide funds for helping to clean these landfills, or perhaps sponsor research to develop new and
better diapers.
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Chapter 3 Summary, page 47
Copyright © 2011 Nelson Education Ltd. Chapter 3: Molecular Compounds and Intermolecular Forces 3-9
Chapter 3 Questions, pages 48–49
1. d
2. (a) False. The crystalline structure of solid water takes up more space than the structure of liquid water,
causing water to take up more space when it freezes.
(b) False. Raindrops form as beads because of the high value of water’s surface tension that is caused by the
strong hydrogen bonds that form between water molecules.
3. Table 1 Properties for Paper Towel Plastic
Rank of
Property
importance Explanation
reusable
5
This is not an important property. It is not likely that people would
ever want to reuse a used paper towel.
biodegradable
1
This is the most important property. Once disposed of, these paper
towels need to be able to break down.
compostable
2
This is important. If the paper towels are put in composts, it is
worthwhile to have the plastic break down.
recyclable
3
It is unlikely that people would take the trouble to recycle used
paper towels, so this is not important.
upcyclable
4
It is not likely that people would gather used paper towels and use
them to make something.
4. (a) Behaviour of a thin stream of a compound released near a negatively charged acetate strip:
(i) NF3
(ii) CH4
(iii) HI
(b) NF3 and HI are both polar molecules. HI is polar because it is diatomic with two different atoms. NF3 is
polar because its bonds are polar covalent and it is not symmetrical. CH4 is not polar because it is very
symmetrical and its bonds are not highly polar.
5. Table 2 Unknown Compounds
Compound Melting point (°C)
Boiling point (°C)
Force
SCl2
–121 °C
N2
–210 °C
KCl
770 °C
HF
–83 °C
6. (a) biodgradable
(b) function
(c) fossil fuel use
(d) cost
(e) greenhouse emissions
(f) compostable
1
5
1
5
1
1
59 °C
–196 °C
1420 °C
20 °C
conventional plastic
conventional plastic
conventional plastic
conventional plastic
conventional plastic
conventional plastic
5
4
3
3
3
4
dipole–dipole
London dispersion
ionic electrostatic
hydrogen bonds
bioplastic
bioplastic
bioplastic
bioplastic
bioplastic
bioplastic
Copyright © 2011 Nelson Education Ltd. Chapter 3: Molecular Compounds and Intermolecular Forces 310
Unit 1 Questions, pages 50–51
1. a
2. (a) Bohr–Rutherford diagram of oxygen:
(b) How an oxygen atom ionizes:
3. False. The electronegativity difference between carbon and fluorine is 1.4, indicating that a C-F bond is
polar covalent in character.
4. (a) The anion for the ionic compound A2(BC3)4 is BC3. The anion is polyatomic.
(b) If the charge on the anion is –2, the valence of the multivalent cation is +4.
5. (a) The IUPAC name for ZnBr2 is zinc bromide.
(b) The IUPAC name for Pb3P4 is lead(IV) phosphide.
6. Write the chemical formula for the following compounds. (2.4) [K/U] [T/I]
(a) The chemical formula for lithium oxide is Li2 O.
(b) The chemical formula for copper(II) nitride is Cu3N2.
7. Figure 2
8. (a) Water exists as a liquid at room temperature. Not special.
(b) Water exists as a solid, liquid, and gas on Earth’s surface. Special.
(c) Water expands when it freezes. Special.
(d) Water is a common compound with a melting point of over –10 °C. Not special.
(e) Water is a molecular compound with a boiling point of over 80 °C. Special.
(f) Water as a solid floats on liquid water. Special.
(g) Water forms droplets. Special.
Copyright © 2011 Nelson Education Ltd. Chapter 3: Molecular Compounds and Intermolecular Forces 311