Nuclear Chemistry

1
Nuclear Chemistry
2
The stability of the atom

• The vast majority of all atoms are incredibly
  stable and their nucleus never changes.
• However, a small percentage of atoms will have
  their nucleus break apart and give off radiation.
• This breaking apart is called decay.
• Decay can happen naturally or we can force it to
  happen through nuclear reactions.

3
Radioactivity

• One of the pieces of evidence for the fact that
  atoms are made of smaller particles came from the
  work of Marie Curie (1876-1934).
• She discovered radioactivity, the spontaneous
  disintegration of some elements into smaller
  pieces.

4
Radioactive Decay

• Most of the isotopes which occur naturally are
  stable.
• Some unstable isotopes are said to be
  radioactive.
• Radioactive (unstable) isotopes are called
  radioisotopes
• Radioisotopes eventually decay and change into
  more stable forms. The stable form is a
  different element. This process is called
  transmutation.

5

• Often times, when a radioisotope decays and
  becomes stable it will release a particle and
  change into a different element.
• Some radioisotopes release energy by emitting
  radiation during the process of decay.

6
Examples of radioactive isotopes
7
Radioactive Decay
Radioactive decay results in the emission of
either

• an alpha particle (a) a positively charged
• helium isotope contains two neutrons and two
• protons

• a beta particle (b) a high speed electron

• or a gamma ray(g) Electromagnetic radiation
• pure energy called a ray rather than a particle

8
Examples of radioactive decay

• C-14 ? N-14 beta particle
• P-32 ? S-32 beta particle
• I-131 ? Xe-131 beta particle
• U-238 ? Th-234 alpha particle

9
Penetrating Ability
10
(No Transcript)
11
Forcing the atom to split up

• Fission- A reaction in which an atomic nucleus
  of a radioactive element splits by bombardment
  from an external source, with simultaneous
  release of large amounts of energy, used for
  electric power generation.

12
Nuclear Fission

• Fission is the splitting of atoms
• These are usually very large atoms, that they are
  not very stable.

13
(No Transcript)
14
Nuclear Fission POWER

• Currently about 103 nuclear power plants in the
  U.S. and about 435 worldwide.
• 17 of the worlds energy comes from nuclear.

15
Figure 19.6 Diagram of a nuclear power plant.
16
Nuclear Fusion The opposite of Fission

• Fusion
• small nuclei combine
• 2H 3H 4He 1n
• 1 1
  2 0
• Occurs in the sun and other stars has ne

Energy
17

• Fusion
• Excessive heat can not be contained
• Attempts at cold fusion have FAILED.
• Hot fusion is difficult to contain

18
Draw a Double Bubble Map of Fusion and Fission
fusion
fission
Differences Similarities Differences
19
Half-Life

• Chemists are interested in the amount of time it
  takes for elements to decay into another element.
  They use the term half-life to measure the
  time it takes an element to decay.
• HALF-LIFE is the time that it takes for 1/2 a
  sample to decompose.

20
Examples of half life

• Lead-210 has a half life of 22 years.
• If you start with 80 g of Pb-210.
• After 22 years, youll have 40 g of Pb-210
• After 44 years, youll have 20 g of Pb-210
• After 66 years, youll have 10 g of Pb-210
• After 88 years, youll have ______ of Pb-210

21

• Po-218 has a half-life of 3 minutes
• If you start with a sample of 100 g of Po-218
• How much is left after 1 half life? ___
• How much is left after 2 half lives?____
• How much is left after 4 half lives? ____

22
Half-Life
What is the half-life?
Decay of 20.0 mg of 15O. What remains after 3
half-lives? After 5 half-lives?
23

1. What is the half-life?
2. How long is 3 half-lives? How much is left?

24
If we start with 200 atoms of a radioactive
substance, how many would remain after one
halflife?_________ after two half-lives?
_________ after three half-lives? ___________
after four halflives?__________
25

1. What is the half life?
2. How long for 3 half lives?

26

• http//www.hamilton-local.k12.oh.us/Downloads/9-29
  _Half20Life20Worksheet.pdf

27
Kinetics of Radioactive Decay

• For each duration (half-life), one half of the
  substance decomposes.
• For example Ra-234 has a half-life of 3.6
  daysIf you start with 50 grams of Ra-234

After 3.6 days gt 25 grams After 7.2 days gt 12.5
grams After 10.8 days gt 6.25 grams
28
Learning Check!

• The half life of I-123 is 13 hr. How much of a
  64 mg sample of I-123 is left after 39 hours?

29
Effects of Radiation
30
Geiger Counter

• Used to detect radioactive substances

31
(No Transcript)
32
Radiocarbon Dating

• Radioactive C-14 is formed in the upper
  atmosphere by nuclear reactions initiated by
  neutrons in cosmic radiation
• 14N 1on ---gt 14C 1H
• The C-14 is oxidized to CO2, which circulates
  through the biosphere.
• When a plant dies, the C-14 is not replenished.
• But the C-14 continues to decay with t1/2 5730
  years.
• Activity of a sample can be used to date the
  sample.

33
Nuclear Medicine Imaging
Thyroid imaging using Tc-99m
34
Food Irradiation

• Food can be irradiated with g rays from 60Co or
  137Cs.
• Irradiated milk has a shelf life of 3 mo. without
  refrigeration.
• USDA has approved irradiation of meats and eggs.