Section 1.4: Isotopes, Radioisotopes, and Atomic Mass
Tutorial 1 Practice, page 27
1. (a) Given: atomic mass and abundance of the three isotopes of neon
Required: atomic mass of neon
Analysis:
atomic mass = % abundance of isotope 1 (mass of isotope 1) + % abundance of isotope 2 (mass
of isotope 2) + % abundance of isotope 3 (mass of isotope 3)
Solution:
Step 1. Substitute the known values into the equation.
atomic mass = 90.5 % (20 u) + 0.3 % (21 u) + 9.2 % (22 u)
Step 2. Solve the equation.
atomic mass = 20.2 u
Statement: The relative atomic mass of neon is 20.2 u.
(b) Given: atomic mass and abundance of the five isotopes of titanium
Required: atomic mass of titanium
Analysis:
atomic mass = % abundance of isotope 1 (mass of isotope 1) + % abundance of isotope 2 (mass
of isotope 2) + % abundance of isotope 3 (mass of isotope 3) + % abundance of isotope 4 (mass
of isotope 4) + % abundance of isotope 5 (mass of isotope 5)
Solution:
Step 1. Substitute the known values into the equation.
atomic mass = 7.9 % (46 u) + 7.3 % (47 u) + 73.9 % (48 u) + 5.5 % (49) + 5.4 % (50)
Step 2. Solve the equation.
atomic mass = 47.9 u
Statement: The relative atomic mass of titanium is 48 u.
Research This: Radon in the Home, page 28
A. Answers may vary. Sample answer: I think there should be more public awareness about
radon in homes. Methods of promoting public awareness could include government information
campaigns, public-service announcements, information provided to home purchasers, and stories
in the news media.
B. Answers may vary. Sample answer: In my opinion, home inspectors should test for radon
levels in houses on the market. Lung cancer is a serious disease and these tests could prevent
additional deaths from lung cancer. The costs to remove the radon should be part of the
government health budget, because it is not the fault of either the buyer or seller that the radon is
there. Health Canada states that high radon levels are not widespread in Canadian homes, so this
would not require a great amount of tax dollars.
Copyright © 2011 Nelson Education Ltd.
Chapter 1: Atomic Structure and the Periodic Table
1.4-1
Section 1.4 Questions, page 29
1. The Three Isotopes of Hydrogen
Isotope
Number of protons Number of neutrons
hydrogen-1
1
0
hydrogen-2 (deuterium)
1
1
hydrogen-3 (tritium)
1
2
2. It is not possible for a single atom of chlorine to have a mass number of exactly 35.45. The
mass number is the sum of the protons and neutrons in the nucleus of an atom. Since you cannot
have fractions of protons and neutrons, both the number of protons and the number of neutrons
must be whole numbers, so the sum will be a whole number.
3. Ag-107 is more abundant. The average atomic mass of silver is 107.9 u. If the two isotopes
existed in equal abundance, the average atomic mass would be 108 u,
since 50 % (107 u) + 50 % (109 u) = 108 u. The average atomic mass is closer to 107 u,
however, so we can infer that Ag-107 is more abundant.
4. Given: atomic mass and abundance of the three isotopes of silicon
Required: atomic mass of silicon
Analysis:
atomic mass = % abundance of isotope 1 (mass of isotope 1) + % abundance of isotope 2 (mass
of isotope 2) + % abundance of isotope 3 (mass of isotope 3)
Solution:
Step 1. Substitute the known values into the equation.
atomic mass = 92.23 % (28 u) + 4.67 % (29 u) + 3.10 % (30 u)
Step 2. Solve the equation.
atomic mass = 28.108 u
Statement: The relative atomic mass of silicon is 28.1 u.
5. The sum of the percentage abundances must be equal to 100 %. There are only two isotopes,
and the percentage abundance of one is known. To determine the percentage abundance of the
other isotope, simply subtract the percentage of the first isotope from 100 %.
6. The atomic mass of carbon is 12.0107 u. This is the weighted average of the masses of three
isotopes, carbon-12, carbon-13, and carbon-14. Because the value is so close to 12 u, we can
reason that the carbon-12 isotope is the most abundant isotope by far.
7. In an atom of Cl-35, there are 17 protons, 17 electrons, and 18 neutrons (A = 35, Z = 17,
A – Z = 18).
In an atom of Cl-37, there are 17 protons, 17 electrons, and 20 neutrons (A = 37, Z = 17,
A – Z = 20).
8. Isotopes are atoms that have the same number of protons but different numbers of neutrons.
A radioisotope is an isotope with an unstable nucleus that spontaneously decays to produce two
or more smaller nuclei.
Copyright © 2011 Nelson Education Ltd.
Chapter 1: Atomic Structure and the Periodic Table
1.4-2
9. Given: atomic mass and abundance of the two isotopes of potassium
Required: atomic mass of potassium
Analysis:
atomic mass = % abundance of isotope 1 (mass of isotope 1) + % abundance of isotope 2 (mass
of isotope 2)
Solution:
Step 1. Substitute the known values into the equation.
atomic mass = 93.10 % (39 u) + 6.90 % (41 u)
Step 2. Solve the equation.
atomic mass = 20.2 u
Statement: The relative atomic mass 39.1 u.
10. Answers may vary. Sample answer: Three careers in which people handle radioisotopes are
nuclear chemist, radiologist, or radioisotope lab technician. To reduce their exposure to radiation,
these workers use shielding between themselves and the radioactive source, and they keep the
time they are exposed to the radiation to a minimum. They wear protective clothing and never
take that clothing out of the lab. They keep radioactive material away from other materials and
do not eat or drink in areas where radioactive materials are used. They dispose of radioactive
waste carefully.
11. Answers may vary. Sample answer: The Cobalt bomb is a piece of medical equipment that
uses cobalt-60, a radioactive isotope, as a radiation source for the treatment of cancers inside the
body. The Cobalt bomb is simple to use and very effective, so it quickly became a standard
treatment, and it is still used today. Radiation therapy can damage normal cells as well as cancer
cells, leading to side effects such as fatigue, nausea, and skin irritation. Most side effects
disappear after treatment ends, but some damage can be permanent. The potential benefits for the
patient include relief of symptoms caused by the cancer, shrinking of tumors, and the possibility
of being cured.
12. Answers may vary. Sample answer: Most Geiger counters work by sensing a change in
electrical conductivity due to the presence of radiation. Essentially, the Geiger counter consists
of a tube that is filled with a gas like helium, neon, or argon. An electrically-charged, thin, metal
wire is run down the tube. When ionized particles contact the gas in the tube, they collide with
the gas and produce an electron. The electron is attracted to the charged wire in the tube,
colliding with more atoms and ionizing them, creating a charge on the wire. This charge can be
translated into a measure of how much radiation is active in the area.
The clicking noises of a Geiger counter are one way to indicate active radiation. Each
click indicates a separate electrical charge caused by radiation. Geiger counters also use a gauge
to show how much radiation is present. The Geiger counter is highly sensitive because the gas
loses its charge quickly after each collision. This allows a scientist to get a precise measurement
of how much radiation is in the area covered by the Geiger counter.
Geiger counters can be used measure levels of radiation, low levels of cosmic rays, and
locate radioactive minerals.
13. Answers may vary. Sample answer: In 2007 and 2008, contaminated soil at the Cameco plant
sites in Port Hope were found. Since then cleanup efforts by Cameco to remove soil and concrete
from these sites have begun. Material has been transferred to an appropriately licensed industrial
landfill site in the United States and will continue into 2011. Cameco is still putting into action
their Vision 2010 plan to clean up, renew, and rejuvenate its Port Hope conversion facility.
New sites for containment of old wastes are being built as well as new plant facilities.
Copyright © 2011 Nelson Education Ltd.
Chapter 1: Atomic Structure and the Periodic Table
1.4-3
The Canadian Nuclear Safety Commission (CNSC) and other federal departments have
developed and reviewed their Environmental Impact Statement (EIS) and continue to closely
monitor the work that Cameco is doing to guarantee it meets the CNSC’s safety guidelines.
The residents of Port Hope formed a Health Committee. The committee monitors the
proposals and work by Cameco and it takes an active role in what is being done in their
community.
Copyright © 2011 Nelson Education Ltd.
Chapter 1: Atomic Structure and the Periodic Table
1.4-4