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CHAPTER 1
Student Textbook page 24
1. Accuracy is how
close a measurement or calculation is to an expected or accepted
value while precision is the exactness of a measurement.
2. (a) kg (b) g
(c) mL (d) cm or m
(e) m
3. (a) 4 (b) 3
(c) 3
4. (a) 97.88 (b) 3.01 103 km2
(c) 2.0 mL2 (d) 0.12 g/mL
5. (a) Students may say a small graduated cylinder, or an appropriately calibrated
dropper. Those who have been exposed to a pipette should suggest it.
(b) Students may suggest a large beaker or graduated cylinder.
(c) graduated cylinder
(d) graduated cylinder or pipette
6. (a) The graph should show data points that are close to an expected value (high
accuracy) but fairly inexact (low precision)
(b) The graph should show data points that are far from an expected value (low
accuracy) and highly inexact (low precision)
Student Textbook page 28
1. Students should have no difficulty linking evaporation and melting with the addition
of energy, and condensation, freezing, and solidifying with the removal of energy.
2. Sublimation should appear twice: once with the addition of energy (solid to gas) and
once with removal of energy (gas to solid).id gas
3. Students should be able to assess their answers based on the definition of a mixture
(i.e., components retaining their own identity). Similarly, their classifications of heterogeneous
and homogeneous mixtures should be based on whether the components
are visible or not.
4. Students should know that water is a pure substance (because electrolysis is required
to separate its component elements). How they know that other substances such as
carbon dioxide, and glucose, are pure substances may be more difficult for them to
explain. Chances are, they know because they have learned that these
substances are made up of elements and that they are not easily separated into their
component elements.
5. Students will likely suggest one or several series of filtering, as well as distillation.
Some students may suggest that a chemical could be added to clean the water (by
precipitation, for example), even if they do not know what chemical that might be.
Accept any reasonable answer.
6. This question provides a good “snapshot” of students’ prior knowledge and critical
thinking skills.
(a) Focus on students’ reasoning here, rather than the correctness of their answers.
Filtering and chemical purifying, for example, are reasonable ideas.
(b) The water likely will not be drinkable. However, some students may know of
chemical products available to campers for making water potable.
(c) Again, the emphasis here should be on reasoning.
Student Textbook pages 29–31
1. (a) chemical (b) physical
(c) physical (d) chemical
2. Physical changes do not alter the composition
of a substance, whereas chemical
changes do.
3. (a) dissolving; physical (b) reactivity; chemical
(c) magnetism; physical (d) freezing point; physical
(e) evaporation; physical (f) decomposition or reactivity; chemical
4. Exp. I: low accuracy, fair precision; Exp. II: low accuracy, low precision; Exp. III: low
accuracy, high precision; Exp. IV: high accuracy, high precision
5. (a) Students’ answers will vary, but should not be more precise than to a single
decimal place for all three containers because none is finely calibrated. Typical
answers could be 125 mL (for A), 3.8 mL (for B), and 40 mL (for C)
(b) Assuming the previous values, approximately 170 mL.
(c) the graduated cylinder, because it is more finely calibrated
6. (a) 1.0 104 g (b) 2.23 10 1 m
(c) 52 cm3 (d) 1.0 103 cm3
7. (a) 1 (b) 4
(c) 1 (d) 2
(e) 5 (f) 4
(g) 5
8. (a) If the value 5700 km were measured accurately, all four digits could be significant.
If rewritten in scientific notation as 5.7 103, only two digits would be significant.
The value could have three significant digits if you consider the fact that the
measured value could be 5769 or 5701.
(b) 5.7 103 km
(c) 5.700 103 km
9. (a) 8.73 mL (b) 1.1 105 m2
(c) 2.2 102 kg/L (d) 0.7
(e) 1.225 104 L (f) 1.8 101 g/mL
10. (a) 6.21 103 (b) 3 101
(c) 6 102 (d) 1.73 101
11. 1.9 104 cm3
12. (a) 24°C
(b) the tenths digit, to the right of the decimal
13. (a) chemical (b) physical
(c) chemical (d) physical
14. (b) Student A
(c) Student D
(d) Student D
15. Pure hydrogen peroxide is a colourless, syrup-like liquid. Exposure to heat, light, and
chemical contaminants cause it to decompose, forming oxygen and water and releasing
heat. In concentrated form, this heat may cause a violent explosion. This property
makes hydrogen peroxide (as a 90% solution) useful as a source of propulsion in
rocket fuel. Pharmacy-available hydrogen peroxide is typically a 3% solution, which is
adequate for safe handling. Nevertheless, any students wishing to experiment with
hydrogen peroxide should observe proper safety precautions. All used solutions
should be returned to you for safe disposal.
Students must recognize that they will be investigating the properties of a solution
of hydrogen peroxide and water. Knowing the physical and chemical properties of
water gives students a control against which they can compare their findings. For
example, students could investigate and compare pharmaceutical hydrogen peroxide
with water in terms of boiling point and freezing point. They can contrast its appearance,
viscosity, “feel”, and (properly) smell with that of water. Chemically, students
could examine questions like: Does hydrogen peroxide react if it is left in sunlight? (It
should bubble.) or Added to a piece of potato? (It does—oxygen bubbles form slowly
on the potato, just as what happens with an open wound, due to the presence of an
enzyme called catalase.)
Students can perform the procedures they design to test their hypotheses if time
permits.
16. Students can use print or electronic resources to “flesh out” their concept webs,
especially for uses of these chemicals.
17. Students likely will design a flowchart similar to the one shown on page 27 of the
student textbook plus identifying aluminum as an element, water as a compound,
cereal as a heterogeneous mixture, and apple juice as a homogeneous mixture.
18. Salad dressing is heterogeneous because the oil and water separate (unless the dressing
includes an emulsifying ingredient that keeps the two mixed).
19. This question is a variation of the Unit 1 Project that appears on page 152 of the student
textbook, and may be easily used as an alternative unit assessment task.
Although this assignment does not require students to come in direct contact with
any chemical products per se, nevertheless, be sure to caution students about safe handling
and proper respect for any chemical products in the home, no matter how
benign they appear to be.
20. Students might suggest questions such as: What is the chemical composition of the
chemical? Does it have a common name by which people know it better? What, precisely,
does it do (i.e., what are its physical and chemical properties)? Where can I go
to learn more about this chemical and the issue that is supposedly associated with it?
(Students questions should indicate some degree of skepticism, as well as a desire to
find out more so that more informed judgments and assessments can be made.)
21. (a) Students will likely identify environmental connections as the most important.
(b) The class may easily split here. Some students may identify societal connections as
most important. Others may choose technology. The selection is much less
important than the reasons students provide for it.
CHAPTER 2
Student Textbook page 39
1. Students’
graphic organizers could take the form of an illustrated version of the
chemical notation they reviewed on page 36. Any student response that clearly shows
the relationship among the table-cell titles should be acceptable.
2. Isotopes are atoms of the same element that differ in the number of neutrons they
possess. Radioisotopes are unstable isotopes that decay spontaneously, releasing
radiation. Students must consult either Chapter 5 or an outside resource to provide
an example. Hydrogen, for example, has three isotopes: hydrogen-1 (“ordinary hydrogen”)
hydrogen-2 (deuterium), and hydrogen-3 (tritium). Tritium is a radioisotope.
3. (a) The first and second pairs have different numbers of protons, electrons, and
neutrons. The third pair has the same number of protons and the same number
of electrons, but a different number of neutrons.
(b) Only the third pair has the same value for Z. Only the first pair has the same
value for A.
4. Dalton said that atoms of one element cannot be converted into atoms of any other
element, which is true for chemical changes. Nuclear reactions, which alter the
atomic nucleus, do in fact convert atoms of one element into atoms of another. Also,
Dalton said that all atoms of one type of element were identical in mass and other
properties. Different isotopes of an element have different masses because they have
different numbers of neutrons.
5. Students’ answers should reflect an awareness that Dalton’s theory still explains a wide
body of observations, but has been modified in light of later understanding. Accept
all reasonable and well-reasoned answers.
Student Textbook page 47
1. The
periodic law states that the chemical and physical properties of the elements
repeat in a regular, periodic pattern when they are arranged according to their atomic
number.
2. alkali metals: Group 1 (Li, Na, K, Rb, Cs, Fr); noble gases: Group 18 (He, Ne, Ar,
Kr, Xe, Rn); halogens: Group 17 (F, Cl, Br, I, At); alkaline earth metals: Group 2 (Be,
Mg, Ca, Sr, Ba, Ra)
3. (a) silicon; antimony; arsenic; bromine
(b) Students should have little difficulty developing additional element descriptions.
4. The number of electrons in each energy level dictates the location of an element in
the periodic table.Precautions
5. The periodic table is divided into 18 columns or groups. The number of valence
electrons in Groups 1, 2, and 3 to 18 is the same as the last numeral in the group
number. For example, Group 1 elements have 1 valence electron, Group 2 elements
have 2, Group 13 elements have 3, Group 14 elements have 4, and so on.
6. (a) neon: 8; bromine: 7; sulfur: 6; strontium: 2; sodium: 1; chlorine: 7; tin: 4;
magnesium: 2; silicon: 4
(b) The Lewis structures for the elements listed in (a) will have the same number of
dots around the elements symbols as the numbers indicated in the answers.
Ne Br
S
Sr
Na Cl
He Sn Mg Si
(c) neon:
non-metal; bromine: non-metal; sulfur: non-metal; strontium: metal;
sodium: metal; chlorine: non-metal; helium: non-metal; silicon: metalloid; tin:
metal; magnesium: metal
7. Two elements are liquid at room temperature: bromine and mercury.
8. The noble gases are very stable, unreactive elements because they have eight electrons
in their outermost energy level (a stable octet electron configuration). No other elements
have this electron configuration.
9. (a) Students will likely suggest that the elements in each triad have similar chemical
and physical properties.
(b) The elements in triads 2 and 3 still appear together in the modern periodic table.
10. Examples include the following:
(a) europium: used in TV screens to produce a red colour
(b) neodymium: used in combination with iron and boron to make powerful magnets
(c) carbon: used to make steel
(d) nitrogen: used to make fertilizers and explosives
(e) silicon: used to make computer chips
(f) mercury: used in mercury vapour lamps
(g) ytterbium: used to improve physical properties of stainless steel
(h) bromine: used in water purification
(i) chromium: used in oil paints to make a red pigment
(j) krypton: used in camera flash lamps
11. (a) Lithium, sodium, and potassium have a single dot, magnesium has two dots,
aluminum has three, and carbon has four.
(b) Sodium, magnesium, and aluminum all have 3 occupied energy levels. Lithium
and carbon both have 2 occupied energy levels.
(c) Lithium, sodium, and potassium all have 1 valence electron.
Li
Na K
Mg Al C
Student Textbook page 56
1. Students
can construct their comparison table by reading carefully the text of the
Chemistry Bulletin. If they wish, students can choose another form of graphic organizer
(or, for that matter, another medium, such as a hyperlinked database) to present
their findings.
2. Bernic Lake is the site of a geological formation known as a pegmatite, which is a
coarse-grained igneous rock that often contains rare elements such as tantalum and
cesium. Students could investigate the geological processes responsible for pegmatite
formation. Students interested in learning the history of the Tanco mine can, with a
little effort, find a four-page brochure on the Internet, available in pdf format.
The current URL is http://www.cabotcorp.com/CWS/Businesses.nsf/CWSID/cws
BUS02042001011331PM6367?OpenDocument&SITE=Specialty_Fluids. The
web page may also be found by accessing the following web page, http://www.cabotcorp.
com/, and typing the word “tanco” in the search box.
Student Textbook page 60
1. (a) Atomic
radius decreases as you move across a period due to the increase of positive
charge of atomic nuclei across a period. Atomic radius increases as you move
down a group due to the additional energy levels that shield valence electrons
from the nucleus.
(b) Ionization energy increases as you move across a period because the attractive force
of the nucleus increases and pulls more tightly on the valence electrons. Ionization
energy decreases as you down a group because the valence electrons are farther
from the attractive force of the nucleus.
(c) Electron affinity follows the same trends as ionization energy, and (in general) for
similar reasons.
2. Note: Students’ explanations involve applying their understanding of group- and
period-related trends.
(a) Cl, S, Mg: increase in atomic size as you move right to left across a period
(b) B, Al, In: increase in atomic size as you move down a group
(c) Ne, Ar, Xe: increase in atomic size as you move down a group
(d) Xe, Te, Rb: increase in atomic size as you move right to left across a period
(e) F, P, Na: increase in atomic size as you move right to left across a period
(f) Ar, Cl, K: increase in atomic size as you move right to left across a period
3. Note: Students’ explanations involve applying their understanding of group- and
period-related trends. This becomes a bit trickier when elements from more than one
group or period are included; however, students are still drawing upon the same
trends for their explanations. This note applies also to question 4 below.
(a) Cl, Br, I
(b) Se, Ge, Ga
(c) Kr, Ca, K
(d) Li, Na, Cs
(e) Cl, Br, S
(f) Ar, Cl, K
4. (a) Ca
(b) Li
(c) Se
(d) Cs
5. This graph shows the trend for atomic radius. The y-axis should be labelled “Atomic
Radius (pm)” and the x-axis should be labelled “Atomic Number”. The graph could
be titled “Atomic Radius v. Atomic Number”. The top line could be labelled “Group
1: Alkali Metals” and the bottom line could be labeled “Group 18: Noble Gases”.
Some students may suggest that all the intervening main-group elements should also
be plotted on the graph—an excellent observation, if it is made.
6. Students may choose to sketch a graph for ionization energy or electron affinity, both
of which will have shapes that are opposite to those shown for question 5. Their
graph lines should resemble those shown below.
Chapter 2 Review Answers
Student Textbook pages 61–63
1. An
atom is the smallest particle of an element that still retains the identity and
properties of that element. An element is a substance that is made up of only a
single type of atom.
2. Students
may provide data in the form of sentences, diagrams, or a chart like the
one below.
3. This is standard notation to show the mass number, atomic number, and symbol for
an isotope of an element. The “O” is the symbol for the element, in this case, oxygen.
The superscript 16 is the mass number of the isotope. The subscript 8 is the atomic
number of the isotope.
4. To calculate the number of neutrons in a neutral atom use the equation:
number of neutrons mass number  atomic number
5. Isotopes are atoms of an element that have the same number of protons, but different
numbers of neutrons and therefore have different atomic masses. Radioisotopes are
unstable isotopes whose nuclei decay releasing energy and subatomic particles.
6. (a) 7 (b) 7 (c) 10 (d) 3–
(e) Se (f) 2– (g) Cr (h) 24
(i) 28 (j) 21 (k) 3+ (l) 19
(m) 9 (n) 9 (o) 9 (p) 0
7. A neutral cobalt atom with an atomic mass of 59 and an atomic number of 27 has
32 neutrons (59  27) and 27 electrons (the same as the number of protons).
8. (a) Hydrogen atoms have an atomic radius of 79 pm which is 7.9 10 11 m.
Thus, the diameter is 15.8 10 11 metres.
Number of hydrogen atoms 1 10 3 m 15.8 10 11 m
6.3 106 H atoms
(b) Potassium atoms have an atomic radius of 235 pm which is 2.35 10 10 m.
Thus, the diameter is 4.70 10 10 metres.
Number of potassium atoms 1 10 3 m 2.35 10 10
4.26 106 K atoms
9. Students’ answers should compare and contrast the following ideas:
10. Students’ name for the periodic table should in some way reflect the regular, repeating
patterns of properties of the elements.
11. (a)
(b) H: Group
1, period 1; Li: Group 1, period 2; N: Group 15, period 2; F:
Group 17, period 1; Co: Group 9, period 4; Ag: Group 11, period 5; Kr:
Group 18, period 4; I: Group 17, period 5; Hg: Group 12, period 6
(c) H: metal; Li: metal; N: non-metal; F: non-metal; Co: metal; Ag: metal; Kr: nonmetal;
I: non-metal; Hg: metal
(d) H: gas; Li: solid; N: gas; F: gas; Co: solid; Ag: solid; Kr: gas; I: solid; Hg: liquid
(e) H: one dot; Li: one dot; N: 5 dots; F: 7 dots; Kr: 8 dots; I: 7 dots. (Note:
Students who are using the first edition of the textbook will be unable to draw
Lewis structures for Co, Ag, and Hg.)
H
Li
12. (a) The
N
F
Co Ag Kr
I
Hg
trend shown could be either for electron affinity or for ionization energy,
because both show the same general direction of increase/decrease.
(b) Students’ sketches should mimic Figure 2.13 (for atomic size) and either 2.17
(ionization energy) or 2.19 (electron affinity).
13. If students “plot” these elements on a blank periodic table, they will see that K and
Rb belong to Group 1; Ca and Sr to Group 2; B and Ga to Group 13; Si and Sn to
Group 14; P and Bi to Group 15; Cl and Br to Group 17.
14. Students could use a generic, labelled Bohr-Rutherford diagram to show the relationship
among these terms. Graphic organizers may also be used. Accept any answer that
clearly shows the relationship.
15. The arrangement of electrons in atoms dictates the periodic trends. For example,
as you move across the periodic table, an extra electron is being added to the atoms.
This causes the atomic radius to decrease and the ionization energy to increase. The
noble gases, with a full octet, are stable and do not give up or accept electrons. The
alkali metals, with only one valence electron, give up this electron (low electron
affinity) and form 1ions. The halogens with 7 electrons gain one electron (high
electron affinity) and form 1– ions.
16. (a) This is very unlikely, because the “new element” would have to have more than
50 and less than 51 protons; no known atoms have fractions of protons.
(b) The questions students ask will vary, but should be direct and should reflect a
skeptical attitude. Nevertheless, the history of science is full of unlikelihood, so
evidence of an open-minded attitude would also be desirable.
17. (a) Students will find most of the data they need in the textbook, but should be
encouraged to consult outside sources such as the CRC Handbook, or any of
several good chemical databases on the Internet. Students should have no trouble
predicting the appearance (colour) of technetium, and should be able to predict
that values for the atomic mass, melting point, and density will likely be between
those of molybdenum and ruthenium, and between those of manganese and rhenium.
Precise values are not required of students here. For quick reference:
(b) One possible prediction for the properties of technetium is:
atomic mass 98.51 u
appearance: silver
melting point 2213°C
density 11.2 g/cm3
Li
Ne
Li
Ne
(c) The actual properties
for technetium are:
atomic mass 98.0 u
appearance: silver
melting point 2157°C
density 11.5 g/cm3
18. Students could set up a table as follows:
19. (a) Students’ answers here must take into account the meaning of the terms listed in
the question, as well as their appearance. Thus, for example, a simple comparison
chart with the listed terms as table fields would only be acceptable if, in one way
or another, explanations of the terms were provided, either in the field itself or as
part of a mini-appendix or summary paragraph below the chart.
(b) This challenging question will provide strong evidence of students’ understanding
of key concepts and terminology from the chapter. Students must not only write
in a style that is suitable for young children, but also frame their explanations to
emphasize meaning (through analogy, perhaps, or metaphor) over terminology.
This question is especially well-suited for gifted students.
20. Both elements have the same number of valence electrons in their outer energy level
because they are both in Group 13 (IIIA).
21. Two sets of elements that would be affected if the elements were arranged in order
of increasing atomic mass: argon and potassium, and cobalt and nickel. If put in
order of increasing atomic mass, argon would be in Group 1 (IA) and potassium
would be in Group 18 (VIIIA). There would be little sense in this arrangement, since
argon has the properties of the noble gases and potassium has the properties of the
alkali metals. Similarly, if put in order of increasing atomic mass, cobalt would be in
Group 10 (VIIIB) and nickel would be in Group 9 (VIIIB). Students will have to do
research to verify their likely inferences that cobalt has more properties in common
with Group 9 elements and nickel has more properties in common with Group 10.
22. Assessment of students’ answers could be informal, though a student-teacher conference,
or more formal, through the use of an essay, oral presentation, or project. The
assessment criteria for Making Connections in the achievement chart could be used
to assess student’s answers.
23. As for question 22, the assessment criteria for Making Connections in the achievement
chart could be used to assess students’ reports.
CHAPTER 3
Student Textbook page 74
1. Ionic
compounds are hard, brittle, crystalline solids with high melting and boiling
points that conduct electricity in the liquid phase. They are usually soluble in water,
and the aqueous solution also conducts electricity. Examples include sodium chloride,
sodium bromide, potassium iodide, and copper(II) sulfate.
2. Covalent compounds are gases, liquids or soft solids with low melting points. They
do not conduct electricity as a liquid or in solution. Some are water soluble (e.g.
sucrose) some are not (e.g. paraffin wax). Examples are water, carbon dioxide, and
ethanol.
3. Students’ answers should include the idea that electronegativity is a trend that
applies only to atoms involved in bonding. Students should note that, in general,
electronegativity increases across a period and decreases down a group. They may
note that the trend for electronegativity is essentially the opposite of the trend for
atomic size. In other words, the smaller the atom, the greater the electronegativity,
in general. This makes sense intuitively, since electrons can get much closer to, and
are therefore more attracted to, atoms with small radii. (Note that this is a simplified
explanation, but it may help students remember the trend.)
4. (a) Li, La, Zn, Si, Br
(b) Cs, Y, Ga, P, Cl
5. (a) EN EN O  EN N 3.44  3.04 0.40 , covalent
(b) EN EN O  EN Mn 3.44  1.55 1.89 , ionic
(c) EN EN Cl  EN H 3.16  2.20 0.96 , covalent
(d) EN EN Cl  EN Ca 3.16  1.00 2.16 , ionic.
6. (a) The melting point of the unknown solid would be low. Since the compound does
not conduct electricity as a liquid, it is a covalent compound. Covalent solids tend
to have low melting points.
(b) As described in the answer to part (a), the compound contains covalent bonds.
Student Textbook page 84
1. (a) MgF2
(b) KBr
(c) RbCl
Rb Cl
[Rb]
[ Cl ]
[K]
[ Br ]

K
Br

Mg
F
F
[Mg]


[ F ]
[ F ]
(d) CaO
2. (a) SO2
(b) HCl3
(c) N2
(d) C2H4O
3. (a) EN EN O
(b) EN EN Br 
 EN Pd 3.44  2.20 1.24 , covalent
EN C 2.96  2.55 0.41, covalent
(c) EN EN S  EN Ag 2.58  1.93 0.65 , covalent
(d) EN EN I  EN Na 2.66  0.93 1.73 , ionic
(e) EN EN F  EN Be 3.98  1.57 2.42, ionic
(f) EN EN P  EN Ca 2.19  1.00 1.19 , covalent
4. This statement is true, because in general, the farther away elements are from one
another, the greater is the difference in their electronegativity, and the more likely
they are to form ionic bonds. Students should note that noble gases are an exception,
since they do not participate in ionic bonding.
5. Atoms joined by covalent bonds share electrons to achieve a stable octet. The
electrons in these bonds are localized, spending most of their time between the two
atoms, and do not move to create a current.
Metallic bonding involves electron sharing, but there are insufficient electrons to
make a stable octet for any of the atoms. Metal ions are surrounded by a “sea” of
shared valence electrons. The electrons are not localized, as a result, and can therefore
carry a current.
6. (a) The ions in an ionic solid are arranged so that the individual ions bond in
three dimensions with ions of the opposite charge. The strong electrostatic
attraction holds the ions rigidly in position, resulting in a hard crystal that
holds its shape.
(b) Ionic solids are not made into tools because:
(i) they dissolve in water, so could not be allowed to get wet;
(ii) they are brittle and shatter easily. A strong blow can shift the ions, so that ions
of the same charge are aligned, which causes the crystal to shatter.
Student Textbook page 94
1. (a) B–F, EN EN F  EN B 3.98  2.04 1.94, ionic
(b) C–H, EN EN C  EN H 2.55  2.20 0.35, covalent
(c) Na–Cl, EN EN Cl  EN Na 3.16  0.93 2.23 , ionic
(d) Si–O, EN EN O  EN Si 3.44  1.90 1.54, polar covalent
(e) S–O, EN EN O  EN S 3.44  2.58 0.86 , polar covalent
(f) C–Cl, EN EN Cl  EN C 3.16  2.55 0.61 , polar covalent
2. (d) Si O 
(e) S O 
(f) C Cl 

Student Textbook page 94
Unit Project Prep
3. A non-polar molecule can
have polar bonds if the symmetry of the molecule is such
that the polarities of the bonds cancel each other out, e.g., in CO2 (OCO), the
two equal but opposite dipoles add to give a net polarity of zero.
4. (a) O–F, H–BR, H–Cl, K–Br
(b) C–H, C–Br, C–O, C–F
5. (a) EN 0.54, 0.76, 0.96, 2.14
(b) EN 0.35, 0.41, 0.89, 1.43
6. Students will respond that chloroform,
CHCl3 , is polar since all dipoles are not
equal, and do not cancel. In methane, CH4, the polarities of all bonds are equal and
thus cancel. As a result, chloroform is slightly polar and the molecules will attract,
giving it a higher boiling point than the non-polar methane. A second reason is that
with the more massive chlorine atoms present in chloroform, there will be more
attraction between the molecules regardless of polarity, e.g. CCl4 is still a liquid at
room temperature. This is, in fact, the more significant effect. Note: In early print
runs, CHCl3 is incorrectly identified as formaldehyde.
7. (a) SiCl4, EN EN Cl  EN S 1.26, polar covalent
The Lewis structure indicates that the molecule is tetrahedral. This means that the
bond polarities will cancel, and the molecule is non-polar.
(b) PCl3, EN EN Cl  EN P 1.13, polar covalent
The Lewis structure indicates that the molecule is trigonal pyramidal. Therefore,
the bond polarities will not cancel, and the molecule will be polar. Note: part (c),
which appears in the first print run of the text, has been cut from subsequent
print runs as the question is too advanced.
8. Accept all reasonable, well-written answers. Students may suggest some of the following
possible effects of non-polar water. Under present conditions, water would be a
gas, not a liquid, so a different substance would have to be the fluid of life; perhaps a
hydrocarbon such as octane, found in gasoline. If temperatures on Earth were such
that non-polar water was a liquid, the solid form of water would sink in its liquid
instead of floating as ice does. This means that lakes, rivers, ponds, etc. would freeze
solid in winter, limiting life as we know it. Aquatic life would have to adapt to survive
the winter differently than they do now. Oxygen gas would be less soluble in the
fluid of life in the non-polar water world, so a better oxygen absorption mechanism
and an efficient metabolism would be required.