Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
247
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 24
forces because a strong nuclear force, which acts only on subatomic particles that are extremely close together, overcomes the
electrostatic repulsion. Because neutrons have no charge but are subject to the strong nuclear force, they add an attractive force to the
nucleus, which is a key to nuclear stability.
For atoms with a low atomic number (Ͻ20), nuclei with a
neutron-to-proton ratio of 1:1 tend to be the most stable. Helium
( 4
2 He) is an example of an atom with a 1:1 neutron-to-proton ratio.
However, as atomic number increases, more neutrons are needed to
produce a nuclear force that is strong enough to balance the electrostatic repulsion forces produced by the protons. This means that the
neutron-to-proton ratio increases to about 1.5:1 for the largest atoms.
Example Problem 24-1
Calculating Neutron-to-Proton Ratio
What is the neutron-to-proton ratio of 210
84 Po?
First calculate the number of neutrons in the nucleus.
Number of neutrons ϭ Mass number – Atomic number
Number of neutrons ϭ 210 Ϫ 84 ϭ 126
Then, calculate the neutron-to-proton (n/p) ratio.
n/p ratio ϭ
ϭ
ϭ
The neutron-to-proton ratio of 210
84 Po is 1.5:1.
Practice Problems
3. Calculate the neutron-to-proton ratio for each of the following
isotopes.
a. 12
6 C
b. 32
16 S
c. 222
86 Rn
d. 234
90 Th
Figure 24–7 on page 866 of your textbook shows a graph of the
number of neutrons versus the number of protons for all known stable nuclei. The slope of the graph shows that more neutrons are
needed to stabilize a nucleus as it increases in size. The area on the
graph within which all the known stable nuclei are found is called
the band of stability. Radioactive nuclei are located outside this
band. When a radioactive nucleus decays, the product is closer to or
1.5
ᎏ
1
126
ᎏ
84
Number of neutrons
ᎏᎏᎏ
Number of protons
Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
247
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 24
forces because a strong nuclear force, which acts only on subatomic particles that are extremely close together, overcomes the
electrostatic repulsion. Because neutrons have no charge but are subject to the strong nuclear force, they add an attractive force to the
nucleus, which is a key to nuclear stability.
For atoms with a low atomic number (Ͻ20), nuclei with a
neutron-to-proton ratio of 1:1 tend to be the most stable. Helium
( 4
2 He) is an example of an atom with a 1:1 neutron-to-proton ratio.
However, as atomic number increases, more neutrons are needed to
produce a nuclear force that is strong enough to balance the electrostatic repulsion forces produced by the protons. This means that the
neutron-to-proton ratio increases to about 1.5:1 for the largest atoms.
Example Problem 24-1
Calculating Neutron-to-Proton Ratio
What is the neutron-to-proton ratio of 210
84 Po?
First calculate the number of neutrons in the nucleus.
Number of neutrons ϭ Mass number – Atomic number
Number of neutrons ϭ 210 Ϫ 84 ϭ 126
Then, calculate the neutron-to-proton (n/p) ratio.
n/p ratio ϭ
ϭ
ϭ
The neutron-to-proton ratio of 210
84 Po is 1.5:1.
Practice Problems
3. Calculate the neutron-to-proton ratio for each of the following
isotopes.
a. 12
6 C
b. 32
16 S
c. 222
86 Rn
d. 234
90 Th
Figure 24–7 on page 866 of your textbook shows a graph of the
number of neutrons versus the number of protons for all known stable nuclei. The slope of the graph shows that more neutrons are
needed to stabilize a nucleus as it increases in size. The area on the
graph within which all the known stable nuclei are found is called
the band of stability. Radioactive nuclei are located outside this
band. When a radioactive nucleus decays, the product is closer to or
1.5
ᎏ
1
126
ᎏ
84
Number of neutrons
ᎏᎏᎏ
Number of protons