Question

section 24.2 radioactive decay
in your textbook, read about the changes that take place in an atomic nucleus when it decays.
circle the letter of the choice that best completes the statement.

1. the number of stable isotopes that exist compared to the number of unstable isotopes is

a. much less. b. much more. c. slightly more. d. about the same.

1. a lightweight isotope is likely to be stable if the ratio of protons to neutrons in its nucleus is

a. 1:2. b. 1:1. c. 2:1. d. 5:1.

1. the only nucleon among the following is the

a. electron. b. positron. c. beta particle. d. neutron.

1. the isotope least likely to be found in the band of stability among the following is

a. $_6^{13}$c. b. $_8^{17}$o. c. $_{13}^{32}$al. d. $_{14}^{29}$si.

1. the isotope formed by the beta decay of $_{19}^{40}$k has an atomic number of

a. 18. b. 39. c. 20. d. 21.

1. the isotope formed by the alpha decay of $_{92}^{238}$u has a mass number of

a. 234. b. 236. c. 238. d. 240.

1. the positron produced during positron emission comes from a(n)

a. neutron. b. proton. c. electron. d. positron.

1. during electron capture, a proton in the nucleus of an atom is converted into a(n)

a. neutron. b. positron. c. electron. d. another proton.

1. when the isotope $_{91}^{238}$pa decays by beta emission, the isotope formed is

a. $_{90}^{234}$ac. b. $_{90}^{239}$th. c. $_{92}^{237}$u. d. $_{92}^{238}$u.

1. the isotope formed by the alpha decay of $_{66}^{154}$dy is

a. $_{66}^{150}$dy. b. $_{67}^{150}$ho. c. $_{64}^{150}$gd. d. $_{67}^{154}$ho.

1. the neutron - to - proton ratio for the isotope sodium - 23 is

a. 1.1:1. b. 1.1:1. c. 2.1:1. d. 1:2.1.

1. the decay of $_{69}^{169}$tm yields $_{68}^{169}$er and

a. $_2^4$he. b. e-. c. γ. d. e+.

1. atoms located above the band of stability on a graph of numbers of neutrons versus number of protons are usually unstable because they contain too many

a. protons. b. neutrons. c. electrons. d. nucleons.

Explanation:

Step1: Recall stability of isotopes

There are far more unstable isotopes than stable ones in nature. So for question 1, the answer is a. much less.

Step2: Recall proton - neutron ratio for stable isotopes

For lightweight isotopes, a proton - neutron ratio of 1:1 is likely to result in stability. So for question 2, the answer is b. 1:1.

Step3: Define nucleon

Nucleons are protons and neutrons. Among the options, neutron is a nucleon. So for question 3, the answer is d. neutron.

Step4: Analyze isotopes in band of stability

$^{29}_{14}Si$ has an unusual neutron - proton ratio compared to the others and is least likely to be in the band of stability. So for question 4, the answer is d. $^{29}_{14}Si$.

Step5: Understand beta decay

In beta decay of $^{40}_{19}K$, a neutron changes to a proton and an electron is emitted. The atomic number increases by 1, so it becomes 20. For question 5, the answer is c. 20.

Step6: Recall alpha decay

In alpha decay of $^{238}_{92}U$, an alpha particle ($^{4}_{2}He$) is emitted. The mass number decreases by 4, so it becomes 234. For question 6, the answer is a. 234.

Step7: Know positron emission

In positron emission, a proton changes into a neutron and a positron. So the positron comes from a proton. For question 7, the answer is b. proton.

Step8: Understand electron capture

During electron capture, a proton in the nucleus combines with an electron to form a neutron. For question 8, the answer is a. neutron.

Step9: Analyze beta - emission decay

When $^{238}_{91}Pa$ decays by beta - emission, a neutron changes to a proton and an electron is emitted. The atomic number increases by 1 and the mass number remains the same, forming $^{238}_{92}U$. For question 9, the answer is d. $^{238}_{92}U$.

Step10: Recall alpha decay

In alpha decay of $^{154}_{66}Dy$, an alpha particle ($^{4}_{2}He$) is emitted. The atomic number decreases by 2 and the mass number decreases by 4, forming $^{150}_{64}Gd$. For question 10, the answer is c. $^{150}_{64}Gd$.

Step11: Calculate neutron - proton ratio

For sodium - 23 ($^{23}_{11}Na$), there are 11 protons and 12 neutrons. The neutron - proton ratio is $\frac{12}{11}\approx1.1:1$. For question 11, the answer is b. 1.1:1.

Step12: Analyze decay products

The decay of $^{162}_{69}Tm$ to $^{158}_{67}Er$ is an alpha - decay as the mass number decreases by 4 and the atomic number decreases by 2. The product is $^{4}_{2}He$. For question 12, the answer is a. $^{4}_{2}He$.

Step13: Understand stability graph

Atoms above the band of stability on a neutron - proton graph usually have too many neutrons. For question 13, the answer is b. neutrons.

Answer:

1. a. much less
2. b. 1:1
3. d. neutron
4. d. $^{29}_{14}Si$
5. c. 20
6. a. 234
7. b. proton
8. a. neutron
9. d. $^{238}_{92}U$
10. c. $^{150}_{64}Gd$
11. b. 1.1:1
12. a. $^{4}_{2}He$
13. b. neutrons