NUCLEAR CHEMISTRY

Nuclear chemistry is the study of the structure of atomic nuclei and the changes they undergo. Nuclear Radiation

The Discovery of Radioactivity Marie Curie named the process by which materials such as uranium give off rays radioactivity; the rays and particles emitted by a radioactive source are called radiation.

As you may recall, isotopes are atoms of the same element that have different numbers of neutrons. Types of Radiation Isotopes of atoms with unstable nuclei are called radioisotopes.

Types of Radiation These unstable nuclei emit radiation to attain more stable atomic configurations in a process called radioactive decay. During radioactive decay, unstable atoms lose energy by emitting one of several types of radiation.

Types of Radiation The three most common types of radiation are alpha (α), beta (β), and gamma ( γ ).

Alpha, Beta or Gamma? ?? Types of Radiation

?? Types of Radiation Negatively charged beta particles are deflected toward the positively charged plate.

?? Types of Radiation Positively charged alpha particles are deflected toward the negatively charged plate. Alpha particles are deflected less than beta rays because they are more massive.

?? Types of Radiation Gamma rays, which have no electrical charge, are not deflected.

Alpha The charge of an alpha particle is 2+ due to the presence of the two protons. An alpha particle (α) has the same composition as a helium nucleus—two protons and two neutrons—and is therefore given the symbol.

Because of their mass and charge, alpha particles are relatively slow-moving compared with other types of radiation. Thus, alpha particles are not very penetrating—a single sheet of paper stops alpha particles. Alpha

Beta A beta particle is a very-fast moving electron that has been emitted from a neutron of an unstable nucleus. Beta particles are represented by the symbol The zero superscript indicates the insignificant mass of an electron in comparison with the mass of a nucleus.

The –1 subscript denotes the negative charge of the particle. Beta radiation consists of a stream of fast-moving electrons. Beta

Because beta particles are both lightweight and fast moving, they have greater penetrating power than alpha particles. A thin metal foil is required to stop beta particles. Beta

Gamma As you can see from the symbol, both the subscript and superscript are zero. Gamma rays are high-energy (short wavelength) electromagnetic radiation. They are denoted by the symbol.

Thus, the emission of gamma rays does not change the atomic number or mass number of a nucleus. Gamma rays almost always accompany alpha and beta radiation, as they account for most of the energy loss that occurs as a nucleus decays. Gamma

Name Symbol Formula Mass Charge Description β α γ high energy radiation Types of Radiation alpha beta gamma high speed electrons helium nuclei He e

Radioactive nuclei undergo decay in order to gain stability. Nuclear Stability All elements with atomic numbers greater than 83 are radioactive.

Balancing a Nuclear Equation Nuclear equations are used to show nuclear transformations. Balanced nuclear equations require that both the atomic number and the mass number must be balanced.

X A Z Atomic number Mass number Element symbol Balancing a Nuclear Equation X Z A

When beryllium-9 is bombarded with alpha particles (helium nuclei), a neutron is produced. The balanced nuclear reaction is given as: Be + He  n ??? Balancing a Nuclear Equation

On the reactant side, the mass numbers equal (9 + 4) = 13. Be + He  n ??? Balancing a Nuclear Equation On the product side, the mass number equals 1. The product side needs an additional 12 for the mass number.

On the reactant side, the atomic numbers equal (4 + 2) = 6. Be + He  n ??? Balancing a Nuclear Equation On the product side, the atomic number equals 0. The product side needs an additional 6 for the atomic number.

The atomic number (the number on the bottom) determines the identity of the element. Be + He  n ??? Balancing a Nuclear Equation 12 6

Be + He  n Balancing a Nuclear Equation 12 6 The element with an atomic number of 6 is carbon. C

When nitrogen-14 is bombarded with a neutron, a proton is produced. The balanced nuclear equation can be written as: N + n  p ??? Balancing a Nuclear Equation

On the reactant side, the mass numbers equal (14 + 1) = 15. Balancing a Nuclear Equation On the product side, the mass number equals 1. The product side needs an additional 14 for the mass number. N + n  p ???

On the reactant side, the atomic numbers equal (7 + 0) = 7. Balancing a Nuclear Equation On the product side, the atomic number equals 1. The product side needs an additional 6 for the atomic number. N + n  p ???

The atomic number (the number on the bottom) determines the identity of the element. N + n  p ??? Balancing a Nuclear Equation 14 6

N + n  p Balancing a Nuclear Equation 14 6 The element with an atomic number of 6 is carbon. C

Th  + He Balancing a Nuclear Equation Balance the nuclear reaction above. Ra???

U  + He Balancing a Nuclear Equation Balance the nuclear reaction above. Th???

Co  + e Balancing a Nuclear Equation Balance the nuclear reaction above. Ni ???

Sometimes you must use atoms other than those on the periodic table to balance nuclear reactions. Balancing a Nuclear Equation

Question What element is formed when undergoes beta decay? Give the atomic number and mass number of the element.

Question Write a balanced nuclear equation for the alpha decay of the following radioisotope.

Question Nitrogen-12 decays into a positron and another element. Write the balanced nuclear equation. N  C + e

Question Uranium-238 is bombarded with a neutron. One product forms along with gamma radiation. Write the balanced nuclear equation. U + n  U + γ

Question Nitrogen-14 is bombarded with deuterium (hydrogen-2). One product forms along with an alpha particle. Write the balanced nuclear equation. N + H  C + He

A half-life is the time required for one- half of a radioisotope’s nuclei to decay into its products. Radioactive decay rates are measured in half-lives. Radioactive Decay Rates

For example, the half-life of the radioisotope strontium-90 is 29 years. If you had 10.0 g of strontium-90 today, 29 years from now you would have 5.0 g left. The decay continues until negligible strontium-90 remains. Radioactive Decay Rates

The graph shows the percent of a stontium- 90 sample remaining over a period of four half-lives. With the passing of each half-life, half of the strontium-90 sample decays.

Calculating Amount of Remaining Isotope Iron-59 is used in medicine to diagnose blood circulation disorders. The half-life of iron-59 is 44.5 days. How much of a mg sample will remain after days? ( mg)

Question Cobalt-60 has a half-life of 5.27 years. How much of a 10.0 g sample will remain after years? (0.625 g)

Question Carbon-14 has a half-life of 5730 years. How much of a 250. g sample will remain after 5730 years? (125 g)

Nuclear Fission Heavy atoms (mass number > 60) tend to break into smaller atoms, thereby increasing their stability. Using a neutron to split a nucleus into fragments is called nuclear fission. Nuclear fission releases a large amount of energy and several neutrons.

Since neutrons are products, one fission reaction can lead to more fission reactions, a process called a chain reaction. A chain reaction can occur only if the starting material has enough mass to sustain a chain reaction; this amount is called critical mass. Nuclear Fission

Nuclear Fusion The combining of atomic nuclei is called nuclear fusion. For example, nuclear fusion occurs within the Sun, where hydrogen atoms fuse to form helium atoms.

Nuclear Fusion Fusion reactions can release very large amounts of energy but require extremely high temperatures. For this reason, they are also called thermonuclear reactions.

What is the difference between nuclear fusion and nuclear fission? Question Nuclear fusion is the combining of nuclei to form a single nucleus. Nuclear fission is the splitting of a nucleus into fragments.

Applications and Effects of Nuclear Reactions Geiger counters, scintillation counters, and film badges are devices used to detect and measure radiation.

Applications and Effects of Nuclear Reactions

Geiger counters use ionizing radiation, which produces an electric current in the counter, to rate the strength of the radiation on a scale. Applications of Nuclear Reactions

Film badges are often used to monitor the approximate radiation exposure of people working with radioactive materials. Applications of Nuclear Reactions

Scintillation counters measure ionizing radiation. Applications of Nuclear Reactions

With proper safety procedures, radiation can be useful in industry, in scientific experiments, and in medical procedures. Applications of Nuclear Reactions

Nuclear power plants use the process of nuclear fission to produce heat in nuclear reactors. The heat is used to generate steam, which is then used to drive turbines that produce electricity. Applications of Nuclear Reactions

Nuclear Reactors

A radiotracer is a radioisotope that emits non-ionizing radiation and is used to signal the presence of an element or of a specific substance. Radiotracers are used to detect diseases and to analyze complex chemical reactions. Applications of Nuclear Reactions

Ionizing radiation has many uses. An X-ray is ionizing radiation, and ionizing radiation can be used in medicine to kill cancerous cells. Applications of Nuclear Reactions

Most medical devices require sterilization after they are packaged, and another trend has been the move to sterilization by gamma radiation as opposed to other methods such as ethylene oxide gas. Advantages of gamma irradiation include speed, cost- effectiveness, and the elimination of the need for special packaging. Applications of Nuclear Reactions

Chemical reaction rates are greatly affected by changes in temperature, pressure, and concentration, and by the presence of a catalyst. In contrast, nuclear reaction rates remain constant regardless of such changes. In fact, the half-life of any particular radioisotope is constant. Applications of Nuclear Reactions

Because of this, radioisotopes, especially carbon-14, can be used to determine the age of an object. The process of determining the age of an object by measuring the amount of a certain radioisotope remaining in that object is called radiochemical dating. Applications of Nuclear Reactions

Radiochemical Dating

Any exposure to radiation can damage living cells. Gamma rays are very dangerous because they penetrate tissues and produce unstable and reactive molecules, which can then disrupt the normal functioning of cells. Effects of Nuclear Reactions

The amount of radiation the body absorbs (a dose) is measured in units called rads and rems. Everyone is exposed to radiation, on average 100–300 millirems per year. A dose exceeding 500 rem can be fatal. Effects of Nuclear Reactions