CHAPTER 22 Nuclear Chemistry

1
CHAPTER 22 Nuclear Chemistry
I

• I. The Nucleus
• (p. 701 - 704)

II
III
IV
2
A. Mass Defect

• Difference between the mass of an atom and the
  mass of its individual particles.

4.00260 amu
4.03298 amu
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B. Nuclear Binding Energy

• Energy released when a nucleus is formed from
  nucleons.
• High binding energy stable nucleus.

E mc2
E energy (J) m mass defect (kg) c speed of
light (3.00108 m/s)
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B. Nuclear Binding Energy
Unstable nuclides are radioactive and undergo
radioactive decay.
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Stable Nuclei
6
CHAPTER 22 Nuclear Chemistry
I

• II. Radioactive Decay
• (p. 705 - 712)

II
III
IV
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A. Types of Radiation

• Alpha particle (?)
• helium nucleus

paper
2

• Beta particle (?-)
• electron

1-
lead

• Positron (?)
• positron

1
concrete

• Gamma (?)
• high-energy photon

0
8
B. Nuclear Decay

• Alpha Emission

Numbers must balance!!
9
B. Nuclear Decay

• Beta Emission

• Positron Emission

10
B. Nuclear Decay

• Electron Capture

• Gamma Emission
• Usually follows other types of decay.
• Transmutation
• One element becomes another.

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B. Nuclear Decay

• Why nuclides decay
• need stable ratio of neutrons to protons

DECAY SERIES TRANSPARENCY
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B. Synthetic Elements

• Transuranium Elements
• elements with atomic s above 92
• synthetically produced in nuclear reactors and
  accelerators
• most decay very rapidly

13

• Stop

14
C. Radioactive Dating

• half-life measurements of radioactive elements
  are used to determine the age of an object
• decay rate indicates amount of radioactive
  material
• EX 14C - up to 40,000 years 238U and 40K - over
  300,000 years

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D. Nuclear Medicine

• Radioisotope Tracers
• absorbed by specific organs and used to diagnose
  diseases
• Radiation Treatment
• larger doses are used to kill cancerous cells
  in targeted organs
• internal or external radiation source

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F. Others

• Food Irradiation
• ? radiation is used to kill bacteria
• Radioactive Tracers
• explore chemical pathways
• trace water flow
• study plant growth, photosynthesis
• Consumer Products
• ionizing smoke detectors - 241Am

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Half Life

• The rate at which radioactive nuclides decay is
  dependent upon the amount of the nuclide present
  to begin with.
• Decay rate is usually expressed in terms of half
  life, the amount of time it takes for half of a
  sample to decay.

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Illustrative Example - 20 min. Half Life
Original sample 32 nuclei After 20 min., half
is left. After another 20 min., one fourth is
left. One eighth is left after another 20 min.
Number of atoms
decayed
0
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Another Example
20
C. Half-life

• Half-life (t½)
• Time required for half the atoms of a radioactive
  nuclide to decay.
• Shorter half-life less stable.

21

• The half-life of cobalt-60 is 10.47 minutes. How
  many mg of cobalt-60 remain after 104.7 minutes
  if you start with 10.0 mg?

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C. Half-life
mf final mass mi initial mass n of half-lives
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C. Half-life

• Fluorine-21 has a half-life of 5.0 seconds. If
  you start with 25 g of fluorine-21, how many
  grams would remain after 60.0 s?

GIVEN t½ 5.0 s mi 25 g mf ? total time
60.0 s n 60.0s 5.0s 12
WORK mf mi (½)n mf (25 g)(0.5)12 mf 0.0061
g