Chapter 16

What do we call atoms in which the nuclei undergo spontaneous change?

In an \(\mathrm{n} / \mathrm{p}\) plot, the band of stability curves up above the \(\mathrm{n} / \mathrm{p}=1\) line. Explain why.

Suppose \({ }_{14}^{35} \mathrm{Si}\) undergoes beta emission. Write a nuclear reaction for this spontaneous change.

Suppose \({ }_{20}^{40} \mathrm{Ca}\) is the product of a beta-emission nuclear reaction. What was the parent isotope?

The fluorine isotope \({ }_{9}^{17} \mathrm{~F}\) undergoes positron emission. (a) Write a nuclear reaction for this emission. (b) Where on the band of stability would you expect to find \({ }_{9}^{17} \mathrm{~F}\) ?

The argon isotope \({ }_{18}^{37} \mathrm{Ar}\) undergoes electron capture. (a) Write a nuclear reaction for this process. (b) Where on the band of stability would you expect to find \({ }_{18}^{37} \mathrm{Ar}\) ? (c) What is the daughter nucleus produced?

The magnesium isotope \({ }_{12}^{25} \mathrm{Mg}\) is the daughter isotope created when a radioactive parent isotope undergoes electron capture. What is the full symbol for the parent isotope?

The magnesium isotope \({ }_{12}^{25} \mathrm{Mg}\) is the daughter isotope created when a radioactive parent isotope undergoes positron emission. What is the full symbol for the parent isotope?

Positron emission moves us one step to the left in the periodic table, and alpha emission moves us two steps to the left. Does this mean that, for a given parent isotope, the daughter isotope resulting from two successive positron emissions is the same as the daughter isotope resulting from one alpha emission?

If a radioactive element undergoes a single decay process and transforms into an element two spaces away on the periodic table, which decay process must have taken place? Explain why it could not be any other decay process.

If a radioactive element undergoes a single decay process and transforms into an element one step to the right in the periodic table, did a proton turn into a neutron or did a neutron turn into a proton? What do we call this type of decay?

A rock from an asteroid contains \(2.57 \mathrm{~g}\) of \({ }_{92}^{236} \mathrm{U}\) and \(3.83 \mathrm{~g}\) of \({ }_{82}^{206} \mathrm{~Pb}\). The molar mass of \({ }_{82}^{206} \mathrm{~Pb}\) is \(205.97446 \mathrm{~g} / \mathrm{mol}\), the molar mass of \({ }_{99}^{238} \mathrm{U}\) is \(238.029 \mathrm{~g} / \mathrm{mol}\), and the half- life of \({ }_{92}^{238} \mathrm{U}\) is \(4.46 \times 10^{9}\) years. Assume that all the \({ }_{82}^{206} \mathrm{~Pb}\) came from the radioactive decay of the \({ }_{92}^{238} \mathrm{U}\). (a) How many atoms of each isotope are present in the rock? (b) How many atoms of \({ }_{92}^{238} \mathrm{U}\) were in the rock when it formed? (c) What is the percent of \({ }_{92}^{238} \mathrm{U}\) atoms remaining in the rock compared to when it was first formed? (d) How old is the asteroid?

Complete this nuclear reaction, and state whether it is fission or fusion. $$ { }_{94}^{239} \mathrm{Pu}+{ }_{0}^{1} \mathrm{n} \rightarrow{ }_{38}^{90} \mathrm{Sr}+?+3{ }_{0}^{1} \mathrm{n} $$

What do we mean when we say that an atom has a mass defect?

What do we mean by the binding energy of an atom, and how does it compare to the energy that binds atoms to one another in a covalent bond?

True or false? (a) The number of nucleons in an atom is equal to its atomic number. (b) The number of nucleons in an atom is equal to its mass number. (c) The number of protons in an atom is equal to its mass number minus its atomic number. (d) The number of neutrons in an atom is equal to its mass number minus its atomic number.

Consider these facts regarding two hypothetical nuclei, one heavy and one light: (1) The heavy nucleus has a greater binding energy than the light nucleus. (2) The light nucleus is more stable than the heavy nucleus. Explain how both facts can be true.

Explain in terms of energy why a chemical reaction could never turn lead into gold.

Of all of the elements and all of their isotopes, which would take the most energy to convert its nucleus into isolated nucleons? Explain why.

What in Einstein's energy equation ensures that a tiny mass defect results in a tremendous amount of energy? Explain.

What is a radioactive atom?

True or false? Radioactive atoms have no mass defect or binding energy. Explain.

Why are neutrons thought to be important for making a nucleus stable?

As we go from light atoms to heavier ones, (a) What happens to the neutron-to-proton ratio? (b) Why does the answer to part (a) make sense?

Write the full symbols for the isotopes of oxygen having 8,9, and 11 neutrons.

What is the band of stability, and why do radioactive isotopes appear on it?

Define half-life.

How many half-lives does it take for a \(10-\mathrm{g}\) sample of \({ }_{53}^{123} \mathrm{I}\) to drop to \(0.039 \mathrm{~g} ?\) What length of time is this? [The half-life of \({ }_{53}^{123} \mathrm{I}\) is \(13.1 \mathrm{~h}\). \(]\)

If you were looking to find or create superheavy atoms, approximately what range of atomic number would you expect for their nuclei?

Energy is always released during radioactive decay in the form of kinetic energy of ejected particles and gamma rays. What is the source of this energy?

What is meant by the term radioactive decay?

Write the full symbol for a neutron, a proton, ? electron, and a positron.

Why is a positron referred to as antimatter?

How do we interpret the subscripts for the full symbols of an electron and a positron?

True or false? Radioactive decay ends up changing the elemental identity of the isotope undergoing decay. Explain.

What happens to an atom's nucleus when it undergoes beta emission?

How is it possible for a nucleus to eject an electron when it contains no electrons?

The tantalum isotope \({ }_{73}^{186} \mathrm{Ta}\) is radioactive and decays by converting a neutron to a proton. (a) Where is this atom likely to lie in the band of stability? (b) Write a nuclear reaction for this decay process. (c) Which type of decay is this?

What happens when an atom's nucleus undergoes: (a) positron emission. (b) electron capture. (c) gamma emission.

Is there a difference between the product of \({ }^{53} \mathrm{Fe}\) emitting a positron and the product of \({ }^{53} \mathrm{Fe}\) emitting a beta particle? If yes, explain fully.

The tungsten isotope \({ }_{74}^{162} \mathrm{~W}\) is radioactive and decays by converting a proton to a neutron. (a) Where is this atom likely to lie in the band of stability? (b) Write two nuclear reactions that describe this decay process. (c) Which type of decay is represented by each reaction you wrote in part (b)?

What kind of nucleus would be likely to eject two neutrons and two protons?

What happens to an atom's atomic number and mass number when it undergoes alpha emission?

The thorium isotope \({ }_{90}^{232}\) Th is radioactive and decays by ejecting two protons and two neutrons from its nucleus. (a) Where is this atom likely to lie in the band of stability? (b) Write a nuclear reaction for this decay process. (c) Which type of decay is this?

Name two forms in which energy can be carried away from a nucleus undergoing radioactive decay.

How do you check to see if a nuclear reaction is balanced?

Pockets of trapped helium gas are found near some deposits of radioactive ores. How can you explain this?

What happens to the mass number and the atomic number of an atom when its nucleus: (a) Ejects a beta particle? (b) Ejects a positron? (c) Undergoes electron capture? (d) Ejects an alpha particle?

Thorium-232 decays by the following sequence of emissions: \(\alpha, \beta, \beta, \alpha, \alpha, \alpha, \beta, \alpha, \beta, \alpha\). What is the final product of this sequence of emissions (give its full atomic symbol)?

Explain how simply examining the periodic table allows you to predict the daughter isotope in: (a) Alpha decay (b) Beta decay (c) Positron emission (d) Electron capture