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College Chemistry - Problem Drill 06: Atoms and Molecules
Question No. 1 of 10
Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as
needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
1. The atomic mass is the mass of a specific isotope. It is the total mass of
protons, neutrons and electrons in a single atom. Which sub-atomic particle does
not contribute significantly to the mass of the atom?
Question
(A) Proton
(B) Neutron
(C) Electron
(D) None
(E) All
A. Incorrect!
A proton has a mass of 1 amu and does contribute significantly to the mass of the
atom.
B. Incorrect!
A neutron has a mass of 1 amu and does contribute significantly to the mass of the
atom.
C. Correct!
Good job! The mass of either a proton or neutron is 1 amu. The mass of an electron
is only 0.0005 amu and therefore doesn’t contribute significantly to the mass of the
atom.
Feedback
D. Incorrect!
The mass of a proton is 1 amu, the same for neutron. They contribute significantly
to the mass of the atom.
E. Incorrect!
The mass of an electron is only 0.0005 amu. It therefore doesn’t contribute
significantly to the mass of the atom.
Protons have a mass of 1 amu.
Neutrons have a mass of 1 amu.
Electrons have a mass of 0 amu and therefore do not contribute significantly to
the mass of an atom.
The correct answer is (C).
Solution
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Question No. 2 of 10
Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as
needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
2. An ion is an atom or group of atoms that has acquired a net charge by gaining
or losing one or more electrons. An ion is formed when _____ and _____ are not
equal.
Question
(A) # of protons, # of neutrons.
(B) # of neutrons, # of electrons.
(C) # of electrons, # of protons.
(D) None of these choices.
(E) Mass of one atom of an element, mass of another atom of the element.
A. Incorrect!
An ion has a charge and neutrons do not affect the charge.
B. Incorrect!
An ion has a charge and neutrons do not affect the charge.
C. Correct!
Good job! An ion has a charge and protons and electrons affect charge.
Feedback
D. Incorrect!
Remember, an ion is an atom with a charge.
E. Incorrect!
Atoms of the same element with different masses are isotopes, not ions.
Ions are atoms with a charge (they are not neutral).
Protons have a charge of +1.
Electrons have a charge of -1.
Neutrons are neutral (no charge) and therefore do not affect the charge of the
atom/ion.
The correct answer is (C).
Solution
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Question No. 3 of 10
Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as
needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
3. A complete chemical symbol displays all the information about an atom’s
protons, neutrons and electrons. Such a symbol contains an element symbol,
surrounded by the atomic number, the mass number of the isotope and the charge
of the ion. For the following, give the number of protons (p), neutrons (n) and
electrons (e).
37
17
Question
Cl 1
(A) p
(B) p
(C) p
(D) p
(E) p
=
=
=
=
=
17,
17,
17,
37,
37,
n
n
n
n
n
=
=
=
=
=
37,
20,
20,
20,
17,
e
e
e
e
e
=
=
=
=
=
1
18
16
39
17
A. Incorrect!
The upper left number gives the mass number (protons + neutrons) not neutrons
alone.
B. Correct!
Good job! The protons + neutrons = 37 and the charge = protons – electrons = -1.
Protons = 17. Therefore, electrons = 18.
C. Incorrect!
This would give a +1 charge rather than a -1 charge.
Feedback
D. Incorrect!
The bottom left number is the protons, not the mass number.
E. Incorrect!
The bottom left number is the protons, not the mass number.
The bottom left number is the atomic number, which is the same as the number of
protons. Protons = 17.
The top left number is the mass number, which is (protons + neutrons). 37 = 17 +
neutrons. Neutrons = 20.
The top right number is the charge, where charge = protons – electrons.
-1 = 17 – electrons. Electrons = 18
The correct answer is (B).
Solution
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Question No. 4 of 10
Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as
needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
4. An atom is defined as the smallest component having the chemical properties of
the element. Atoms of the same element can have different numbers of which?
Question
(A) Protons
(B) Neutrons
(C) Electrons
(D) B & C
(E) A & C
A. Incorrect!
Protons define an atom.
B. Incorrect!
Although the number of neutrons can change without changing the identity of the
atom, there is a better option in this problem.
C. Incorrect!
Although the number of electrons can change without changing the identity of the
atom, there is a better option in this problem.
Feedback
D. Correct!
Good job! Both neutrons and electrons can vary in atoms of the same elements.
E. Incorrect!
Option A is incorrect since protons define an atom.
Protons determine the identity of an atom, therefore atoms of the same element
cannot have different number of protons.
Atoms of the same element with different numbers of neutrons are called isotopes.
The number of electrons can change to form atoms with a charge.
The correct answer is (D).
Solution
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Question No. 5 of 10
Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as
needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
5. An atom is a smallest unit of an element. Which of the following is true?
Question
(A) Atoms of the same element are all exactly the same.
(B) Atoms of the same element have the same number of protons.
(C) Atoms of the same element have the same number of neutrons.
(D) B & C
(E) A & B
A. Incorrect!
This is not true as atoms of the same element could have a different number of
neutrons (and therefore a different mass - isotopes).
B. Correct!
Good job! This is true, as the number of protons defines the element.
C. Incorrect!
This is not true as atoms of the same element could have a different number of
neutrons (and therefore a different mass - isotopes).
Feedback
D. Incorrect!
C is not correct! This is not true as atoms of the same element could have a
different number of neutrons (and therefore a different mass - isotopes).
E. Incorrect!
A is incorrect. This is not true as atoms of the same element could have a different
number of neutrons (and therefore a different mass - isotopes).
A is not true as atoms of the same element could have a different number of
neutrons (and therefore a different mass).
B is true as the number of protons defines the element.
C This is not true as atoms of the same element could have a different number of
neutrons (and therefore a different mass).
The correct answer is (B).
Solution
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Question No. 6 of 10
Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as
needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
6. An isotope is any two or more forms of an element with the same number of
protons but different number of neutrons. The atomic mass of hydrogen is 1.01
amu. Which is the mass of the most abundant hydrogen isotope?
Question
(A) 1 amu
(B) 2 amu
(C) 3 amu
(D) They are all present in the same percentage.
(E) It is impossible to determine from the given information.
A. Correct!
Good job! A weighted average is closest to the one that occurs most often.
B. Incorrect!
A weighted average is closest to the one that occurs most often.
C. Incorrect!
A weighted average is closest to the one that occurs most often.
Feedback
D. Incorrect!
A weighted average is closest to the one that occurs most often.
E. Incorrect!
A weighted average is closest to the one that occurs most often.
The atomic mass is the weighted average of the mass of all the isotopes of that
element. A weighted average is closest to the one that occurs most often.
The correct answer is (A).
Solution
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Question No. 7 of 10
Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as
needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
7. When an atom gains or losses one or more electrons, it becomes an ion. An
atom loses an electron. It is now a(n) _____.
Question
(A) Anion
(B) Cation
(C) Isotope
(D) Atom
(E) None of the above
A. Incorrect!
An anion is a negatively charged ion. This results from the gaining of electrons.
B. Correct!
Good job! A cation is a positively charged ion. This results from the loss of
electrons.
C. Incorrect!
An isotope results from differing numbers of neutrons.
Feedback
D. Incorrect!
Once an atom has gained or lost electrons, it is now an ion.
E. Incorrect!
Look again—there is a correct option in the list.
If an atom loses electrons, it now has more protons (positive) than electrons
(negative) and it has an overall positive charge. An ion with a positive charge is a
cation.
The correct answer is (B).
Solution
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Question No. 8 of 10
Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as
needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
8. Carbon has three naturally occurring isotopes: 12C, 13C and 14C. How many
neutrons are in a Carbon-12 atom?
Question
(A) 5
(B) 6
(C) 7
(D) 12
(E) Cannot be determined from the given information.
A. Incorrect!
The mass number “12” is equal to the protons + neutrons.
B. Correct!
Good job! The mass number “12” is equal to the protons + neutrons. Protons = 6.
Therefore neutrons = 6.
C. Incorrect!
The mass number “12” is equal to the protons + neutrons.
Feedback
D. Incorrect!
The mass number “12” is equal to the protons + neutrons.
E. Incorrect!
The mass number “12” is equal to the protons + neutrons.
Carbon is element #6. It therefore has 6 protons.
Carbon-12 has a mass number of 12.
Mass = protons + neutrons.
12 = 6 + neutrons
Neutrons = 6
The correct answer is (B).
Solution
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Question No. 9 of 10
Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as
needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
9. The mass of an atom, with the unit of atomic mass units (amu), is an important
property of an element. The mass on the periodic table is _____.
Question
(A) The mass number.
(B) The number of protons + neutrons.
(C) The atomic mass of the most abundant isotope.
(D) The weighted average of the atomic masses of all the isotopes.
(E) None of the above.
A. Incorrect!
Mass number is the sum of protons + neutrons for a single atom and it is not the
mass shown on the periodic table.
B. Incorrect!
The number of protons + neutrons is the mass number and is for a specific atom.
C. Incorrect!
It’s not only the most abundant element that is taken into account.
Feedback
D. Correct!
Good job! It is the weighted average of the mass of all the isotopes.
E. Incorrect!
Look more closely—there is a correct answer in this question.
The mass of the periodic table is the weighted average of the isotopes of that
element with 4-5 significant figures.
The correct answer is (D).
Solution
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Question No. 10 of 10
Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as
needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
10. Copper is a metal with high thermal and electric conductivity. This metal and
its alloys have been used for thousands of years. It has two isotopes (Cu-63 and
Cu-65). 63Cu has an atomic mass of 62.93 amu and a percent abundance of
69.09%. 65Cu has an atomic mass of 64.94 amu and a percent abundance of
30.91%. Calculate the average atomic mass of copper.
Question
(A) 62.93 amu
(B) 64.83 amu
(C) 63.55 amu
(D) 29 amu
(E) 64 amu
A. Incorrect!
This is the atomic mass of one of the isotope Cu-63. It is not the average atomic
mass.
B. Incorrect!
This is the atomic mass of one of the isotope Cu-65. It is not the average atomic
mass.
C. Correct!
Good job! Take the average of the two isotopes with their percentage contributions.
Keep the same significant figures.
Feedback
D. Incorrect!
This is the atomic number of copper, not atomic mass. Remember Atomic Mass =
Protons + Neutrons.
E. Incorrect!
This should not be a whole number since there are four significant figures given of
all the known data.
The average atomic mass = (0.6909 x 62.93 amu) + (0.3091 x 64.94 amu) =
63.55 amu
Be aware of the significant figures (4) of the final answer.
The correct answer is (C).
Solution
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