UNIT 1 Chapter 2 ELEMENTS AND THE PERIODIC TABLE
Section Review Answers
Student Textbook page 37
■
■
The diameter of a proton or
neutron is 1 × 10−15 m.
Since 1 nm = 1 × 10−9 m,
this would be 1 × 10−6 nm.
Since 1 pm = 1 × 10−12 m,
this would be 1 × 10−3 pm.
Encourage students to be
creative with their analogies. To get students
started, you could offer this
example: If an atom were
as large as a football field,
the nucleus would be
about as large as a baseball at centre field.
Electrons, on this scale,
would be as small as sand
particles.
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.
Element
Atomic
Number
Mass
Number
Number of
Protons
Number of
Electrons
Number of
Neutrons
(a) silver
(b) 47
108
(c) 47
47
(d) 61
(e) arsenic
(f) 33
(g) 75
33
(h) 33
42
(i) bromine
35
(j) 80
(k) 35
(l) 35
45
(m) gold
79
197
(n) 79
(o) 79
(p) 118
(q) tin
(r) 50
(s) 119
(t) 50
50
69
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.
2.2 Atoms, Elements, and the Periodic Table
Student Textbook page 38
For any isotope, it is acceptable to leave out the atomic
number because the atomic
number (the number of protons) for all isotopes of a
particular element will always
be the same. An element’s
symbol, therefore, is always
associated with the same
atomic number.
96
Student Textbook pages 40–48
This section reviews the organization of elements in the periodic table. Students will
learn how to outline the structure of the periodic table in relation to energy levels and
electron arrangement. As a result, students will be able to predict the number of valence
electrons for main-group elements, and represent them using Lewis structures. This
understanding is crucial for the periodic trends that are introduced in the final section of
this chapter.
MHR • Unit 1 Matter and Chemical Bonding
Safety
Precautions
Observing the Spectra of Elements
Please ensure that students
have read Safety in Your
Chemistry Laboratory on pages
x–xiii of the student textbook.
Also ensure that they follow all
safety precautions outlined for
this investigation in the student
textbook.
Student Textbook page 43
Approximate Time Required: 30 min
Tips
■
■
Ensure that gas discharge tubes of at least two elements are available.
You can set up this lab as a series of stations, with one gas discharge tube at each
station. Students can rotate to each station at fixed time intervals.
Answers to Analysis Questions
1. Hydrogen’s spectrum has two violet bands, one green band, and one red band. The
spectrum of an incandescent light bulb is a continuous spectrum, meaning it has all
the colours of the rainbow with no breaks in between the colours. All elements have
their own unique line spectrum (distinct coloured lines separated by darkness).
2. and 3. Hydrogen, with only one electron, produces a faint line spectrum. An atom
with more than one electron would produce a brighter line spectrum.
4. Gas discharge tubes contain gases at that are under low pressure. Street lights contain
different kinds of gases (e.g., sodium, mercury), which, when subjected to electricity,
glow much like gas discharge tubes. Encourage students to explain the benefit of
using the soft yellow-orange colour of sodium lamps (for example) to illuminate
highway road signs, rather than (for example) the more glaring blue-purple colour
of mercury lamps.
Assessment and Evaluation
ThoughtLab/
ExpressLab/
Investigation
Observing the
Spectra of
Elements, page 43
Expectation
■
[MCB 3.01] identify chemical substances and
reactions in everyday use or of environmental
significance
Assessment
Tools/Techniques
■
■
In-class
discussion
Observation
notes
Achievement
Chart Categories
Learning Skills
■
■
■
Communication
Inquiry
■
Organization
Works
independently
Section Review 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.
Chapter 2 Elements and the Periodic Table • MHR
99
UNIT 1 Chapter 2 ELEMENTS AND THE PERIODIC TABLE
5. The periodic table is divided into 18 columns or groups. The number of valence
Student Textbook page 44
■
The book on the top shelf
possesses more potential
energy because it is farther
from the ground and therefore has more gravitational
potential energy.
■
A book cannot be put
between bookshelves.
Nothing is there to hold it.
■
The potential energy of a
book on a higher shelf is
lessened if it is moved to a
lower shelf.
■
This is similar to the way
electrons behave.
Electrons farther from the
nucleus are in a higher
energy level (are on a
higher shelf) and possess
more energy than electrons that are closer to
the nucleus.
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.
Li
Na
K
Mg
Al
C
(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.
100
MHR • Unit 1 Matter and Chemical Bonding
Answers to Conclusion Questions
4. Atomic radius is a periodic property of atoms, because it fairly clearly increases down
each group and decreases across each period.
Answers to Application Questions
5. Students will likely expect to observe the same trend for transition elements.
However, they will discover that the trend is quite irregular and that decreases in size
across a period are far less pronounced than for main-group elements. Students who
require reasons for this irregularity may be invited to investigate the topic of orbitals.
However, the explanations here can become quite involved for elements beyond
period 3, and many students may decide to be content to wait until grade 12 for
more satisfactory explanations.
Assessment and Evaluation
ThoughtLab/
ExpressLab/
Investigation
Investigation 2-A:
Analyzing Atomic
Radius Data,
pages 50–51
Expectation
■
[MCB 2.02] Analyze data involving periodic
properties such as ionization energy and atomic
radius in order to recognize general trends in
the periodic table
Assessment
Tools/Techniques
■
■
■
■
Rubric for
Investigation 2-A
(see
“Assessment
and Evaluation”
in the front
matter of
Teacher’s
Resource
CD-ROM)
Models
Graphs
Analysis of group
predictions
Achievement
Chart Category
■
Inquiry
Chemistry Bulletin
Learning Skills
■
■
Teamwork
Initiative
Figure 2.14
Making Connections
Student Textbook page 53
Student Textbook page 56
Neon has the same electron
arrangement that sodium and
magnesium have. Argon has
the same electron arrangement that sulfide and chloride
ions have.
Answers to Making Connections Questions
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.
Chapter 2 Elements and the Periodic Table • MHR
103
Section Review Answers
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.
Chapter 2 Elements and the Periodic Table • MHR
105
UNIT 1 Chapter 2 ELEMENTS AND THE PERIODIC TABLE
6. Students may choose to sketch a graph for ionization energy or electron affinity, both
Ionization Energy
(MJ/mol)
of which will have shapes that are opposite to those shown for question 5. Their
graph lines should resemble those shown below.
Atomic Number
Chapter 2 Review Answers
Student Textbook pages 61–63
Answers to Knowledge/Understanding Questions
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.
Particle
Charge
Mass (g)
Size (m)
−24
1 × 10 −15
Proton
1+
1.67 × 10
Neutron
0
1.67 × 10 −24
1 × 10 −15
Electron
1−
9.02 × 10 −28
1 × 10 −18
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
106
MHR • Unit 1 Matter and Chemical Bonding
(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:
Dalton’s Atomic Theory
Modern Atomic Theory
All matter is made up of particles called atoms.
An atom cannot be created, destroyed, or
divided into smaller particles.
Each atom is made up of smaller subatomic
particles: protons, neutrons, and electrons.
An atom is divisible, as in “splitting an atom”.
The atoms of one element cannot be converted
into the atoms of any other element.
Nuclear reactions (changes that alter the
composition of the atomic nucleus) do, in
fact convert atoms of one element into atoms
of another.
All the atoms of one element have the same
properties, such as mass and size. These
properties are different from the properties
of the atoms of any other element.
Different isotopes of an element have different
numbers of neutrons and thus different masses.
Atoms of different elements combine in
specific proportions to form compounds.
This idea has remained essentially unchanged.
10. Students’ name for the periodic table should in some way reflect the regular, repeating
patterns of properties of the elements.
11. (a)
18
1
1
H
2
2
13
Li
14
15
N
16
17
F
3
3
4
5
6
7
4
8
9
10
11
12
Co
Kr
5
Ag
6
I
Hg
(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
N
F
Ag
Kr
I
Hg
Co
Chapter 2 Elements and the Periodic Table • MHR
107
UNIT 1 Chapter 2 ELEMENTS AND THE PERIODIC TABLE
12. (a) The 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.
1 valence electron
(valence is 1)
Li
Ne
energy levels
8e–– called
“stable octet”
Li
Ne
8 valence electrons, therefore
filled outer energy level
(valence is 0)
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.
Answers to Inquiry Questions
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:
Element
Atomic Mass (u)
Appearance
Melting Point (˚C)
Density (g/cm3)
manganese
54.94
silver-grey
1245
7.43
molybdenum
95.94
silver
2623
10.22
ruthenium
101.07
silver
2334
12.2
rhenium
186.21
silver
3180
21.02
(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
108
MHR • Unit 1 Matter and Chemical Bonding
(c) The actual properties for technetium are:
atomic mass = 98.0 u
appearance: silver
melting point = 2157˚C
density = 11.5 g/cm3
Answers to Communication Questions
18. Students could set up a table as follows:
Element
Atomic
Number
Mass
Number
Number
of
Protons
Number
of
Neutrons
Number
of
Electrons
Number of
Electrons/Energy
Level
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.
Answers to Making Connections Questions
22. Assessment of students’ answers could be informal, though a student-teacher confer-
ence, 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 2 Elements and the Periodic Table • MHR
109