Chemistry for Changing Times12th Edition

Hill and Kolb

Chapter 11Nuclear Chemistry: The Heart of Matter

John SingerJackson Community College, Jackson, MI

© 2010 Pearson Prentice Hall, Inc.

© 2010 Pearson Prentice Hall, Inc.

11/2

Background Radiation

• Three-fourths of all exposure to radiation comes from background radiation.

• Most of the remaining one-fourth comes from medical irradiation such as X-rays.

© 2010 Pearson Prentice Hall, Inc.

11/3

Radiation Damage to Cells

• Radiation is capable of removing electrons from cells forming ions, hence the term ionizing radiation.

• Molecules can also splinter into neutral fragments called free radicals. Free radicals can disrupt cellular processes.

© 2010 Pearson Prentice Hall, Inc.

11/4

Radiation Damage to Cells

• Radiation often affects the fastest growing cells and tissues such as white blood cells and bone marrow.

• Ionizing radiation can also disrupt DNA causing mutations.

© 2010 Pearson Prentice Hall, Inc.

11/5

Radiation Damage to Cells

© 2010 Pearson Prentice Hall, Inc.

11/6

Nuclear Equations

In nuclear equations, we balance nucleons (protons and neutrons). The atomic number (number of protons) and the mass number (number of nucleons) are conserved during the reaction.

© 2010 Pearson Prentice Hall, Inc.

11/7

Nuclear Equations

Alpha Decay

© 2010 Pearson Prentice Hall, Inc.

11/8

Nuclear Equations

Beta Decay

© 2010 Pearson Prentice Hall, Inc.

11/9

Nuclear Equations

© 2010 Pearson Prentice Hall, Inc.

11/10

Nuclear EquationsPositron emission: A positron is a particle equal in mass to an electron, but with opposite charge.

© 2010 Pearson Prentice Hall, Inc.

11/11

Nuclear Equations

Electron capture: A nucleus absorbs an electron from the inner shell.

© 2010 Pearson Prentice Hall, Inc.

11/12

Nuclear Equations

© 2010 Pearson Prentice Hall, Inc.

11/13

Nuclear Equations

© 2010 Pearson Prentice Hall, Inc.

11/14

Nuclear Equations

© 2010 Pearson Prentice Hall, Inc.

11/15

Half-Life

Half-life of a radioactive sample is the time required for ½ of the material to undergo radioactive decay.

© 2010 Pearson Prentice Hall, Inc.

11/16

Half-Life

© 2010 Pearson Prentice Hall, Inc.

11/17

Half-Life

Fraction remaining = 1/2n

© 2010 Pearson Prentice Hall, Inc.

11/18

Radioisotopic Dating

© 2010 Pearson Prentice Hall, Inc.

11/19

Radioisotopic Dating

Carbon-14 dating: The half-life of carbon-14 is 5730 years. Carbon-14 is formed in the upper atmosphere by the bombardment of ordinary nitrogen atoms by neutrons from cosmic rays.

© 2010 Pearson Prentice Hall, Inc.

11/20

Radioisotopic Dating

Tritium dating: Tritium is a radioactive isotope of hydrogen. It has a half-life of 12.26 years and can be used for dating objects up to 100 years old.

© 2010 Pearson Prentice Hall, Inc.

11/21

Artificial Transmutation

Bombardment of stable nuclei with alpha particles, neutrons, or other subatomic particles cause new elements to form. This process is known as artificial transmutation.

© 2010 Pearson Prentice Hall, Inc.

11/22

Uses of Radioisotopes

Tracers

Radioisotopes can be easily detected through their decay products. Therefore, they can be used to trace their movement. Some uses of tracers include:• Detect leaks in underground pipes.• Determine frictional wear in piston rings.• Determine uptake of phosphorus and its

distribution in plants.

© 2010 Pearson Prentice Hall, Inc.

11/23

Uses of Radioisotopes

Irradiation of Food

Radioisotopes can destroy microorganisms that cause food spoilage.

© 2010 Pearson Prentice Hall, Inc.

11/24

Nuclear Medicine

Radiation therapy: Nuclear radiation can be used to kill cancerous cells. Radiation is most lethal to fastest growing cells. Radiation is aimed at the cancerous tissue. Patients undergoing radiation therapy often experience nausea and vomiting, which are early signs of radiation sickness.

© 2010 Pearson Prentice Hall, Inc.

11/25

Nuclear MedicineDiagnostic Uses of Radiation

© 2010 Pearson Prentice Hall, Inc.

11/26

Nuclear Medicine

Gamma ray imaging: Technetium-99m emits gamma radiation. It can be used to image the heart and other organs and tissues.

© 2010 Pearson Prentice Hall, Inc.

11/27

Nuclear Medicine

Positron Emission Tomography (PET): A patient inhales or is injected with positron-emitting isotopes such as carbon-11 or oxygen-15. When positrons encounter electrons, they emit two gamma rays, which exit the body in opposite directions. PET scans can be used to image dynamic processes.

© 2010 Pearson Prentice Hall, Inc.

11/28

Penetrating Power of Radiation

• Alpha radiation is least penetrating and can penetrate the outer layer of skin. Alpha radiation is stopped by a sheet of paper.

• Beta radiation can penetrate through a few cm of skin and tissue. Beta radiation is stopped by a sheet of aluminum foil.

• Gamma radiation will pass right through a body. Gamma radiation requires several cm of lead to stop.

© 2010 Pearson Prentice Hall, Inc.

11/29

Penetrating Power of Radiation

© 2010 Pearson Prentice Hall, Inc.

11/30

Penetrating Power of Radiation

Two means of protecting one’s self from radiation are distance and shielding.

Distance: Move away from the source. The intensity of radiation decreases with increasing distance from the source.

Shielding: Lead is a commonly used shield for radiation.

© 2010 Pearson Prentice Hall, Inc.

11/31

Energy from the Nucleus

By 1905, Albert Einstein had developed his famous mass–energy equation:

E = mc2

E = Energy

m = Mass

c = Speed of light

© 2010 Pearson Prentice Hall, Inc.

11/32

Energy from the Nucleus

When protons and neutrons combine to form a nucleus, a small amount of mass is converted into energy. This is known as binding energy.

© 2010 Pearson Prentice Hall, Inc.

11/33

Binding Energy

© 2010 Pearson Prentice Hall, Inc.

11/34

The Building of the BombNuclear fission: Fission occurs when larger nuclei split into small nuclei.

© 2010 Pearson Prentice Hall, Inc.

11/35

Nuclear Chain Reaction

Fission of one nucleus produces neutrons that can cause the fission of other nuclei, thus setting off a chain reaction.

© 2010 Pearson Prentice Hall, Inc.

11/36

Manhattan Project

The Manhattan Project was launched by President Roosevelt in 1939. It consisted of four separate research teams attempting to:

• Sustain the nuclear fission reaction• Enrich uranium• Make fissionable plutonium-239• Construct a fission atomic bomb

© 2010 Pearson Prentice Hall, Inc.

11/37

Manhattan Project

Atomic Bomb

© 2010 Pearson Prentice Hall, Inc.

11/38

Manhattan Project

Mushroom cloud over Nagasaki from the detonation of “Fat Man,” August 9, 1945.

© 2010 Pearson Prentice Hall, Inc.

11/39

Radioactive Fallout

Many radioactive isotopes are produced in a nuclear bomb blast. Some are particularly harmful to humans. Among these are strontium-90 and iodine-131.Strontium-90: Has a half-life of 28.5 years and is chemically similar to calcium. It is obtained from dairy and vegetable products and accumulates in bone.Iodine-131: Has a half-life of 8 days. It concentrates in the thyroid glands.

© 2010 Pearson Prentice Hall, Inc.

11/40

Nuclear Power Plants

Civilian nuclear power plants use less enriched uranium (2.5-3.5% uranium-235 rather than 90% for weapons).

The nuclear chain reaction is controlled for the slow release of heat energy. The heat is used to make steam, which turns a turbine to produce electricity.

© 2010 Pearson Prentice Hall, Inc.

11/41

Thermonuclear Reactions

Nuclear fusion is a thermonuclear reaction. Smaller atomic nuclei are fused into larger nuclei in such a reaction. The principle reaction on the sun is one such reaction.

© 2010 Pearson Prentice Hall, Inc.

11/42

The Nuclear Age