CHEM101 Study Guide

Unit 8: Nuclear Chemistry


8a. Distinguish different types of nuclear decay

  • What are the characteristics of an alpha particle?
  • What are the characteristics of a beta particle?

There are two main types of nuclear decay.

An alpha particle is a type of nuclear decay that is equivalent to a helium nucleus:  ^4 \, _2He . When this type of decay occurs, the atomic number of the product will be reduced by two.

A beta particle is a high-energy electron. During beta particle decay, the neutron decomposes into a beta particle and a hydrogen nucleus,  ^1 \, _1H . When this type of decay occurs, the atomic number of the product is increased.

Review this material in Radioactive Decay, Alpha Decay, Beta Decay, and Types of Decay.


8b. Balance nuclear equations

  • Can you balance nuclear equations?

To balance a nuclear equation, we must account for how the emission of nuclear particles changes the nucleus of the atom.

Alpha particle decay will reduce the mass number of the product by four and the atomic number by two.

_{92}^{238}\textrm{U}\;\rightarrow \;_{90}^{234}\textrm{Th}\;+\; _{2}^{4}\textrm{He}

When balancing a nuclear equation, be sure that the mass number and the atomic number sum to the same amount on both sides of the equation arrow. For example, identify the missing species when isotope 212-Po decays to isotope 208-Pb.

212-Po has a mass of 212 and an atomic number of 84.
208-Pb has a mass of 208 and an atomic number of 82.

The mass and atomic numbers must sum to the same amount on both sides of the equation arrow. Thus, the product side is missing a mass of 4 (208 + 4 = 212) and an atomic number of 2 (82 + 2 = 84). If an alpha particle is added to the product side, this will balance the nuclear equation.

_{84}^{212}\textrm{Po}\;\rightarrow \;_{82}^{208}\textrm{Pb}\;+\; _{2}^{4}\textrm{He}

Beta particle decay will keep the mass number constant but will increase the atomic number by one.

_{53}^{131}\textrm{I}\;\rightarrow \;_{54}^{131}\textrm{Xe}\;+\; _{-1}^{0}\textrm{ }\beta

Review this material in Alpha-Decay, Beta-Decay, and Writing Nuclear Equations.


8c. Explain the process of radioactive dating

  • What is half-life?
  • How does radioactive dating work?

Radioactive dating is an important technique that takes advantage of the known half-lives and natural abundances of radioisotopes. All radioactive isotopes decay in a predictable pattern. We define the term half-life as the time it takes for half of a sample of a radioactive isotope to decay to its daughter element. Half-lives are known and are constant for different isotopes. This decay occurs in a predictable pattern, as seen below.

We can write a rate equation for the rate of radioactive decay:

k=\frac{In\left [ 2 \right ]}{t_{1/2}}=\frac{0.693}{t_{1/2}}

(k is called the rate constant, and t_{1/2} is the half-life of the isotope).

From this equation, we can determine the ratio of the concentration of the isotope at a certain time, Ct to the initial concentration of the isotope, C_{0} by the equation:

In\: \frac{C_{0}}{C_{1}}=kt

This allows us to determine how much of a radioactive isotope will remain after a certain amount of time has passed.

The most common type of isotope dating is carbon dating, which is used for determining the age of archeological and other artifacts. In carbon dating, the age of carbon-containing material is determined by comparing the decay rate of that material with living material.

Carbon-14 decays by the following reaction:

_{6}^{14}\textrm{C}\rightarrow _{7}^{14}\textrm{N}+_{-1}^{0}\textrm{e} with a half-life of 5.73 \times 10^{3} years

Review this material in Half-Life and Carbon Dating.


8d. Contrast the processes of nuclear fission and fusion

  • What is nuclear fission?
  • What is nuclear fusion?

The two types of nuclear reactions are nuclear fission and nuclear fusion.

In nuclear fission, a large nucleus is split by being hit by a high-energy neutron. This creates two new atoms, which each continue to form new atoms and neutrons if there is sufficient energy. This is known as a chain reaction, which produces an immense amount of energy. Nuclear fission reactions were used in the atomic bombs.

Nuclear fusion, by contrast, is the process of combining small nuclei together to form a larger nucleus. The simplest example of this is combining two deuterium (hydrogen isotope) atoms to form helium:

_{1}^{2}\textrm{H}+_{1}^{2}\textrm{H}\rightarrow _{2}^{4}\textrm{He}

This produces significantly more energy than nuclear fission. Nuclear fusion is what takes place in the sun and other stars because they have sufficient hydrogen reserves to sustain the reaction.

Review this material in Transmutation of the Elements, Mass Defect, Nuclear Fission, and Nuclear Fusion.


8e. Explain the risks and benefits of nuclear energy

  • How is nuclear chemistry used to produce energy?

Nuclear power is a source of energy for many people all over the world. In nuclear power plants, a nuclear fission chain reaction takes place to produce energy. The reaction rate is controlled by control rods that absorb excess neutrons produced in the chain reaction without undergoing nuclear fission reactions themselves. These control rods are made of different metals and alloys. The nuclear material is kept in fuel rods which are placed between the control rods. By moving the control rods, the rate of nuclear reaction in the fuel rods can be controlled. The energy from the nuclear reaction is put through a heat exchanger to create steam to turn a turbine.

The most common radioactive material used in nuclear reactors is the isotope uranium-235.

Review a description of some of the considerations in using nuclear power in Nuclear Energy and LibreText Nuclear Energy.


Unit 8 Vocabulary

  • Alpha particle
  • Beta particle
  • Carbon dating
  • Chain reaction
  • Control rod
  • Daughter element
  • Fuel rod
  • Half-life
  • Nuclear decay
  • Nuclear fission
  • Nuclear fusion
  • Radioactive dating
  • Rate equation