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Concept evaluations by chapter
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CHAPTER 1
Atoms and elements
1. A teacher asks her students to represent the following chemical reaction, using Dalton’s atomic
model:
2 H2 + O2  2 H2O
Here are four of the representations the teacher received:
a)
c)
b)
d)
Which representation follows Dalton’s model?
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2. Thomson made many observations using cathode ray tubes.
a) What are cathode rays composed of?
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b) Based on his discoveries, Thomson modified Dalton’s atomic model. What was wrong with
Dalton’s model?
c) Complete the diagram opposite by adding
the signs of the charges needed to deflect the
cathode rays downward.
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3. The diagram opposite represents the results
of one of Rutherford’s experiments. The
arrows show the possible trajectories of
alpha particles when a sheet of gold foil is
bombarded with them.
a) What are alpha particles?
b) Which arrow represents the trajectory most often observed during the experiment? Explain
your answer.
c) Why was Rutherford so surprised by the results of his experiment?
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4. Bohr studied the light emitted by various elements by decomposing it to observe their visible
emission spectra.
a) What do the bands of colour in the emission spectra of the elements represent?
b) Why do different elements emit bands of different colours?
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d) Based on his discoveries, Rutherford modified Thomson’s atomic model. What was wrong
with Thomson’s model?
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c) Based on his discoveries, Bohr modified Rutherford’s atomic model. What was wrong with
Rutherford’s model?
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5. Neon is an element with the atomic number 10 and a relative atomic mass of 20.28 u.
a) Since the atomic number of neon is 10, the atoms of this element contain 10 protons and
10 electrons. Given that the mass of a proton is approximately 1 u and the mass of an
electron is negligible compared to that of a proton, why is the relative atomic mass of neon
not approximately 10 u?
b) Neon has three natural isotopes:

neon-20, with a relative atomic mass of approximately 20 u

neon-21, with a relative atomic mass of approximately 21 u

neon-22, with a relative atomic mass of approximately 22 u
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Which of these three isotopes is most commonly found in nature? Explain your answer.
c) Draw a simplified atomic model of each of the natural isotopes of neon.
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d) The simplified atomic model improved on the Rutherford-Bohr model. What was wrong with
the Rutherford-Bohr model?
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6. Where in the periodic table can you find the following:
a) an alkaline earth metal?
b) a noble gas?
c) a halogen?
d) a metal?
e) an atom containing only one
electron shell?
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A.
C.
E.
B.
D.
F.
a) Write the name of each of the six elements on the line under the model.
b) Write the atomic numbers and the chemical symbols for the six elements in the appropriate
boxes in the table below.
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7. Six different elements are represented below according to the Rutherford-Bohr atomic model.
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c) Do all these elements belong to the same period? Explain your answer.
d) Which of these elements are good conductors of electricity? Explain your answer.
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8. Mendeleev developed his periodic classification of the elements at a time when some of the
elements had not yet been discovered. Since he believed in the periodicity of properties, he
formulated certain predictions about the properties of unknown elements. For example, he
predicted that the atomic mass of an element with the atomic number 32 would be 72 u and
that its density would be 5.5 g/mL. Refer to the periodic table and to Appendix 1 of the student
book to see whether Mendeleev’s predictions were accurate, and write your findings below.
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9. Which characteristic of the atom explains its chemical properties?
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10. What are the atomic numbers of the following elements?
a) Its nucleus contains six protons and eight neutrons.
b) An atom contains 10 electrons and 11 neutrons.
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11. If you know the AZ E notation of an atom of an element, how can you determine:
a) the number of electrons it contains?
b) the number of neutrons it contains?
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EST 12. Which of the following elements are isotopes of the same element? Explain your answer.
22
10E
a) 2012 E
b) 2211 E
c)
d) 1912 E
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13. What properties do all the isotopes of a single element share?
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EST 14. Natural silver is made up of two isotopes in almost equal proportions. Their atomic masses are
107 u and 109 u, respectively. What is the relative atomic mass of silver?
EST
15. Boron, which has an atomic mass of 10.81 u, is a mixture of two isotopes, which occur
in a ratio of 20 to 80 percent. The mass number of one of these isotopes is 11.
a) What is the mass number of the other isotope?
b) Which of the two isotopes is more common?
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16. Identify the following elements and write their names using AZ E notation.
a) an element with 12 protons and 12 neutrons
b) an element with 16 neutrons and a mass number of 31
c) an element that is a liquid at 25°C and that has a
relative atomic mass of 80 u
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17. Draw a Rutherford-Bohr atomic model of the
element in the second row and the sixth
column of the periodic table. Remember to
write the name of the element.
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18. Draw a Lewis structure for each of the following elements. Remember to write the names of
the elements.
a) I am a noble gas belonging b) I am the lightest halogen. c) I am the smallest of the
to the third period.
atoms with four valence
electrons.
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19. Draw a Rutherford-Bohr atomic model for each of the following elements. Remember to write
the names of the elements.
b) I am an alkali metal with
three electron shells.
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a) I am the first element in
the group of alkali metals.
c) I am a halogen with one
electron shell more than
fluorine.
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20. Draw a simplified atomic model for each of the following elements. Remember to write the
names of the elements.
a) I am the smallest metal
b) I am an atom with six
c) I am the smallest of the
with three valence
valence electrons and
alkaline earth metals.
electrons.
three electron shells.
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21. Are the following statements true or false? If a statement is false, correct it.
a) A mole corresponds to a certain quantity of matter.
b) The molar mass of molecular nitrogen (N2) is 14.01 g.
c) The mass of 6.02  1023 molecules of water is 18.02 g.
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22. One of the lakes of Tibet contains the second largest lithium deposit in the world. This element
is used extensively today in cellphone batteries and will also be used, in the near future, in
batteries for hybrid or electric cars. In 2008, one battery out of every four sold in the world was
manufactured in China. China therefore has a certain economic interest in Tibet. Mining the
resource is relatively simple: a salt (lithium carbonate) dissolved in the lake water is recovered,
and the lithium is extracted.
a) Given that 0.2 mol of lithium carbonate weighs 14.8 g, which of the following chemical
formulas correctly represents a molecule of this salt? Show your calculations.
A. LiCO3
B. Li2CO3
C. LiCO2
D. Li3CO
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b) How many molecules does a 370-g sample of this salt contain? Show your calculations.
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[ _____ /90]
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