Chem 1075 Chapter 18 Nuclear Chemistry Lecture Outline Slide 2 ...

Chem 1075 Slide 2

Chapter 18

Nuclear Chemistry

Lecture Outline

Natural Radioactivity

• There are three types of radioactivity: 1. Alpha particles (a) are identical to __________________ nuclei, containing _____protons and ______neutrons. Represented by: 2. Beta particles (b) are identical to ___________________ but come from the ____________________ __________________ neutron in the nucleus.

3. Gamma rays (g) are high energy light. Represented by:

Slide 3

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Slide 4

Charge of Radiation types

_______________ particles have a ________ charge and _____________ particles have a ______ charge. Both are ____________________________ by an electric field. _________________rays are electromagnetic radiation and have _________charge, so they are _________________________________ Behavior of Radiation

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Since alpha particles have the _________________________________, they are the ____________ moving type of radiation. Gamma rays move at the ___________________________ since they are electromagnetic radiation. Atomic Notation

A nuclide is the ________________________ of a specific atom. The radioactive nuclide strontium-90 has a mass number of ________ (or 90 protons + neutrons total). The atomic number is __________.

Represented as: Slide 6

Nuclear Reactions

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A nuclear reaction involves a ________________________ change in an atomic ______________. For example, a uranium-238 nucleus changes into a thorium-231 nucleus by releasing a helium-4 particle, and a large amount of energy.

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In a balanced nuclear reaction, the ________________________and _______________________for the reactants must ___________________those of the products.

Slide 7

Balancing Nuclear Reactions

1. The total of the atomic numbers (____________________) on the ______________________ of the equation must ________________the sum of the atomic numbers on the ______________________. 2. The total of the atomic masses (______________________) on the _____________________ of the equation must ________________the sum of the atomic masses on the _______________________. 3. After completing the equation by writing all the nuclear particles in atomic notation, a coefficient may be necessary to balance the reaction. Slide 8

Common Nuclear Particles


Slide 9

Alpha Emission

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Radioactive nuclides can decay by giving off an alpha particle.

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Radium-226 decays by alpha emission.

Slide 10

Beta Emission

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Some radioactive nuclides decay by beta emission. Radium-228 loses a beta particle to yield actinium-228.

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Beta decay is originates from the decay of a ___________________ into a proton and an electron.

Slide 11

Gamma Emission

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Gamma rays often accompany other nuclear decay reactions. For example, uranium-233 decays by releasing both alpha particles and gamma rays.

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Note that a gamma ray has a mass and a charge of _____________, so it has _________________ on the nuclear reaction.

Slide 12

Positron Emission

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A positron (β+) has the mass of an electron but a ______ charge. During positron emission, a _________________ decays into a neutron and a positron.

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Sodium-22 decays by positron emission to neon-22.

Slide 13 •

Electron Capture

A few large, unstable nuclides decay by electron capture. A heavy, _________________________ charged nucleus attracts an electron.


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The electron combines with a proton to produce a ________________. Lead-205 decays by electron capture.

Slide 14 • • •

Some ___________________________ nuclides must go through a series of decay steps to reach a nuclide that is __________________. This stepwise disintegration of a radioactive nuclide until a stable nucleus is reached is called a radioactive decay series. For example, uranium-235 requires 11 decay steps until it reaches the stable nuclide lead-207.

Slide 15

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Uranium-238 Decay Series

Uranium-238 undergoes _____ decay steps before it ends as stable lead-206. The decay series for uranium-238 is shown here. The series includes ____________________________ and _______________________________

Slide 16 •

Decay Series

Parent & Daughter Nuclides

The term parent-daughter nuclides describes a _________________ nuclide decaying into a resulting ____________________ nucleus. For example, the first step in the decay series for U-238 is:


Slide 17 Activity • The number of nuclei that disintegrate in a given period of time is called the activity of the sample. • A ______________________________ is used to count the activity of radioactive samples. • Radiation ___________________gas in a tube which allows ________________________________ _______________________________ • This causes a _____________________ to be heard and the number of disintegrations to be counted. Slide 18 Half-Life Concept • The level of radioactivity for all radioactive samples ____________________ over time. • Radioactive decay shows a __________________________________________________________. • If we start with a sample that has an activity of 1000 disintegrations per minute (dpm), the level will drop to 500 dpm after a ____________________________________. After the ________________ amount of time, the activity will drop to 250 dpm. • The amount of time for the activity to __________________________________ is the half-life, t½. Slide 19

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Half-Life

After each half-life, the activity of a radioactive sample drops to ______________its previous level. A decay curve shows the activity of a radioactive sample over time.

Slide 20

Half-Life Calculations

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A sample of plutonium-239 waste from a nuclear reactor has an activity of 20,000 dpm. How many years will it take for the activity to decrease to 625 dpm? The half-live for Pu-239 is 24,000 years.

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Iodine-131 is used to measure the activity of the thyroid gland. If 88 mg of I-131 are ingested, how much remains after 24 days (t½ = 8 days).


Slide 21 • • • •

Artificial Radioactivity

A larger nuclide (“__________________________________”) can be converted into another element by bombarding it with a smaller particle (“_____________________________________”). This process is called ______________________________________. The elements beyond uranium on the periodic table do ____________________________________ and have been made by transmutation. For example, rutherfordium can be prepared from californium:

Slide 22

Balancing Nuclear Reactions

Balance the following reactions. Then identify whether they are natural decay or transmutations:

U → ____ + 24He + 00γ

233 92

U → ____ + 8 24He + 6 −10e

238 92 22 11

Na → ____ +

____ → 14 7

0 +1

e

Rn + 24He

222 86

N + 01n → ____ + 11H

205 82

Pb + ____ →

205 81

249 98

Cf + ____ →

257 104

Tl Rf + 4 01n

Slide 23 Half-life Practice • If 160mg of technetium-99 is administered for a medical diagnosis, how much of the nuclide remains after 24 hours? (t1/2=6 hrs)

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A nuclear fission reactor produces Sr-90 as radioactive waste. If 20 half-lives are required for the nuclide to reach a safe level, how long must the nuclear waste be stored? (t1/2=28.8 yrs)

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If an iron-59 sample has an initial activity of 200 dpm, how much time is required for the activity to drop to 25dpm? (t1/2=45 days)
