Ch. 28 Nuclear Chemistry

C. Smith

I. Nuclear Radiation• A. Radioactivity

• 1. Radioisotopes are unstable isotopes that have unstable nuclei.

• 2. They gain stability by undergoing changes involving emissions of large amounts of energy.

• 3. Nuclear reactions are not affected by changes in temperature, pressure, or the presence of a catalyst.

• 4. French chemist Antoine Becquerel accidentally discovered the ability of uranium salt to cause unexposed film to fog.

• 5. Becquerel and his associates Marie and Pierre Curie showed that the fogging of the plates was caused by rays emitted by the uranium ore.

I. Nuclear Radiation• A. Radioactivity

• 6. Marie Curie named the process by which material gives off ray radioactivity.

• 7. The penetrating rays are called radiation.• 8. Unstable radioisotopes have too many or too few

neutrons in relation to protons in the nucleus.• 9. Unstable nucleus lose energy by emitting radiation

during a process of radioactive decay.• 10. Eventually, unstable radioisotopes of one element are

transformed into stable (nonradioactive) isotopes of a different element.

• 11. Radioactive decay is spontaneous and does not require an input of energy.

I. Nuclear Radiation• B. Types of Radiation

• 1. There are three types of radiation.• a. Alpha radiation (α)• b. Beta radiation (β)• c. Gamma radiation (ϒ)

• 2. Alpha radiation consist of helium nuclei emitted from a radiation source.

• 3. Alpha particles contain two protons and two neutrons and have a double positive charge.

• 4. The sum of the mass numbers (superscripts) must equal the sum on the left and the same goes for the atomic number.

• 5. When an atom loses an alpha particle, the atomic number of the product atom is lower by two and its mass number is lower by four.

I. Nuclear Radiation

• B. Type of Radiation• 6. Because of their large mass and charge, alpha particles do

not tend to travel very far and are not very penetrating. • 7. Alpha particles are easily stopped by a sheet of paper or

the surface of your skin but are dangerous when ingested and can damage soft tissue.

• 8. Beta Particles are fast moving electrons formed by the decomposition of a neutron in an atom.

• 9.The neutron decomposes into a proton and the electron is released.

• 10. Beta particles have a subscript of -1 and a mass of zero.

I. Nuclear Radiation• B. Type of Radiations

• 11. Gamma radiation is high energy electromagnetic radiation.

• 12. They are often emitted along with alpha and beta particles.

• 13. They have no mass and no charge and does not alter the atomic mass or number.

• 14. X-ray are examples of gamma radiation.

I. Nuclear Radiation• Alpha Radiation:

U23892 Th234

90 He42 +

He42

I. Nuclear Radiation• Beta Decay:

I

+ e

0−1 e0

−1or

Xe13154

+

0−1

13153

I. Nuclear Radiation• C. Other Types of Radiation

• 1. Positron Emission- Loss of a positron (a particle that has the same mass as but opposite charge than an electron). e0

1

C116 B11

5 + e01

207 207

I. Nuclear Radiation• C. Other Types of Radiation

2. Electron Capture (K-Capture)-Addition of an electron to a proton in the nucleus. As a result, a proton is transformed into a neutron.

p11 + e0

−1 n10

II. Nuclear Transformations• A. Nuclear Stability and

Decay• 1. The stability of a nuclei

depends on the neutron-to-proton ratio.

• 2. For elements of low atomic number (below 20), the ratio is about 1 which means that they have roughly equal numbers of neutrons and protons.

• 3. The ratio is 1.5 for heavy elements.

• 4. Band of Stability and Radioactive Decay - The shaded region in the figure shows what nuclides would be stable, the so-called belt of stability.

II. Nuclear Transformations• A. Nuclear Stability and Decay

• 5. As nuclei get larger, it takes a greater number of neutrons to stabilize the nucleus.

• 6. All nuclei with atomic number greater than 83 are radioactive.

• 7. These nuclei tend to decay by alpha emission.

• 8. Nuclei above this belt have too many neutrons.

• 9. They tend to decay by emitting beta particles.

• 10. Nuclei below the belt have too many protons.

• 11. They tend to become more stable by positron emission or electron capture.

• 12. Large radioactive nuclei cannot stabilize by undergoing only one nuclear transformation.

• 13. They undergo a series of decays until they form a stable nuclide (often a nuclide of lead).

II. Nuclear Transformations• B. Half-Life

• 1. Half-Life is the time that it takes for Half-Life is the time that it takes for 1/2 a sample to decompose.1/2 a sample to decompose.

• 2. The rate of a nuclear transformation 2. The rate of a nuclear transformation depends only on the “reactant” depends only on the “reactant” concentration.concentration.

II. Nuclear Transformations• C. Transmutation Reactions

• 1. The conversion of one element to another element is called transmutations.

• 2. Radioactive decay is one of the ways that transmutation occur.• 3. It can also happen when high energy particles bombard the nucleus.• 4. Some transmutations occur in nature such as carbon-14 from nitrogen-

14.• 5. The elements with the atomic number 92 and above are called

transuranium elements and all undergo transmutation.• 6. None of these elements occur in nature and they are all radioactive.

III. Fission and Fusion of Atomic Nuclei• A. Nuclear Fission

• 1. When nuclei of certain isotopes are bombarded with neutrons, they undergo fission.

• 2. Fission is the splitting of a nucleus into smaller fragments.• 3. Uranium-235 and Plutonium-239 are fissionable material.

III. Fission and Fusion of Atomic Nuclei

A. Nuclear Fission

4. Fission chain has three general steps:4. Fission chain has three general steps:

a. Initiation. Reaction of a single atom starts the a. Initiation. Reaction of a single atom starts the

chain (e.g., chain (e.g., 235235U + neutron).U + neutron).

b. Propagation. b. Propagation. 236236U fission releases neutrons that U fission releases neutrons that

initiate other fissions.initiate other fissions.

c. c. Neutrons released in the transmutation strike

other nuclei, causing their decay and the production of

more neutrons which causes a chain reaction. .

III. Fission and Fusion of Atomic Nuclei• A. Nuclear Fission

• 5. Fission can be controlled so energy is released more slowly.

• 6. Nuclear reactors are examples of controlled fission.• 7. There are two ways to control fission reactions:

• a. Neutron Moderation• b. Neutron Absorption

• 8. Neutron moderation • a. The process of reducing the speed of neutrons so that

they can be captured by the reactor fuel in order to continue the chain reaction.

• b. Water and carbon are usually the medium because the neutrons are moving too fast and will pass through without being absorbed.

III. Fission and Fusion of Atomic Nuclei

• A. Nuclear Fission• 9. Neutron Absorption

• a. The process of decreasing the number of slowed neutrons by trapping them in control rods.

• b. Cadmium is used as control rods.

• c. Raising and lower the control rods slows or speed up the

reaction in the core.

III. Fission and Fusion of Atomic Nuclei• B. Nuclear Fusion

• 1. Nuclear fusion is when nuclei combine to produce a nucleus of greater mass.

• 2. The sun is an example of nuclear fusion.• 3. The problem with nuclear fusion is achieving the

high temperatures needed to start the reaction.• 4. Another problem is that matter involved exist in

a plasma state and no structural matter can withstand containment.

III. Fission and Fusion of Atomic Nuclei• C. Nuclear Waste

• 1. Spent fuel rods from reactors are a one major source of nuclear waste.

• 2. They are classified as high-level waste.• 3. Some waste exists for a short period of

time while other waste can remain for thousand of years.

• 4.Low-level waste is taken to licensed burial sites that are monitored and controlled by the Department of Transportation