Unformatted text preview: Chemistry I – Chapter 25
Chemistry I Honors –
ICP – Chapter 18
ICP 1 Nuclear Chemistry SAVE PAPER AND INK!!! When
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(Tools>Options>Print>UNcheck Radioactivity 2 • One of the pieces of evidence for the
fact that atoms are made of smaller
particles came from the work of
• She discovered ________, the
spontaneous disintegration of some
elements into smaller pieces.
elements Nuclear Reactions vs.
Normal Chemical Changes
Normal 3 • Nuclear reactions involve the nucleus
• The nucleus opens, and protons and
neutrons are rearranged
• The opening of the nucleus releases a
tremendous amount of energy that holds
the nucleus together – called binding
• “Normal” Chemical Reactions involve
electrons, not protons and neutrons
electrons Mass Defect
• Some of the mass can be converted into
• Shown by a very famous equation!
Speed of light 4 5 Types of Radiation
• Alpha (ά) – a positively
charged helium isotope - we
2 He usually ignore the charge because it involves
electrons, not protons and neutrons
electrons, •Beta (β) – an electron
•Gamma (γ – pure energy;
called a ray rather than a
0 e γ 6 Other Nuclear Particles
0 n • Positron – a positive
+1 e •Proton – usually referred to
•Any other elemental isotope 1
1 H 7 Penetrating Ability 8 Balancing Nuclear Reactions
•In the reactants (starting materials –
on the left side of an equation) and
products (final products – on the right
side of an equation)
Atomic numbers must balance
Mass numbers must balance
•Use a particle or isotope to fill in the
missing protons and neutrons 9 Nuclear Reactions
• Alpha emission Note that mass number (A) goes down by 4
and atomic number (Z) goes down by 2.
Nucleons (nuclear particles… protons and
neutrons) are rearranged but conserved 10 Nuclear Reactions
• Beta emission Note that mass number (A) is unchanged
and atomic number (Z) goes up by 1. 11 Other Types of Nuclear Reactions
Positron (0+1β ): a positive electron 207 Electron capture: the capture of an electron
Electron 207 12 Learning Check
What radioactive isotope is produced in the
following bombardment of boron?
10 B 5 + 4He
2 ?+ 1 n 0 13 Write Nuclear Equations!
Write the nuclear equation for the beta
emitter Co-60. 14 Artificial Nuclear Reactions
New elements or new isotopes of known elements
are produced by bombarding an atom with a
subatomic particle such as a proton or neutron
-- or even a much heavier particle such as 4He
Reactions using neutrons are called
Reactions γ reactions because a γ ray is usually emitted.
Radioisotopes used in medicine are often made by
γ reactions. 15 Artificial Nuclear Reactions
Example of a γ
Example reaction is production 31
of radioactive 31P for use in studies of P
for uptake in the body.
15 P+ 1
0 n --->
---> P+γ 32
15 Transuranium Elements
Elements beyond 92 (transuranium) made
starting with an γ reaction
92 U+ n --->
92 ---> 239
92 U 239
93 U+γ 1
0 Np --->
Np Np + 0-1β
94 Pu +
Pu β 0
-1 16 Nuclear Fission 17 Nuclear Fission 18 Fission is the splitting of atoms
These are usually very large, so that they are not as stable Fission chain has three general steps:
1. Initiation. Reaction of a single atom starts the
chain (e.g., 235U + neutron) 2. Propagation.
236 U fission releases neutrons that
fission initiate other fissions
3. ___________ .
3. 19 Stability
• Out of > 300 stable isotopes:
N Even Odd Even 157 52 Odd 50 5 Z 19
9 F 31
15 P 2 H, 63Li, 105B, 147N, 18073Ta
H, Li, 10 B, 14 N, 180 1 Band of Stability
Decay 20 Representation of a fission process. 21 Nuclear Fission & POWER
• Currently about 103
nuclear power plants in
the U.S. and about 435
• 17% of the world’s
energy comes from
nuclear. 22 Figure 19.6: Diagram of a nuclear power plant. 23 24 Nuclear Fusion Fusion
small nuclei combine
2 H 1 3 + 4 H 1 1 He 2 + n+
0 Occurs in the sun and other stars Energy 25 Nuclear Fusion
• Excessive heat can not be contained
• Attempts at “cold” fusion have
• “Hot” fusion is difficult to contain 26 Half-Life
• HALF-LIFE is the time that it takes for 1/2
a sample to decompose.
• The rate of a nuclear transformation
depends only on the “reactant”
concentration. Half-Life 27 15
Decay of 20.0 mg of 15O. What remains after 3 half-lives?
After 5 half-lives?
After 28 Kinetics of Radioactive Decay
For each duration (half-life), one half of the
For example: Ra-234 has a half-life of 3.6 days If you start with 50 grams of Ra-234
After 3.6 days > 25 grams
After 7.2 days > 12.5 grams
After 10.8 days > 6.25 grams 29 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? Effects of Radiation 30 31 Geiger Counter
• Used to detect radioactive substances 32 Radiocarbon Dating 33 Radioactive C-14 is formed in the upper atmosphere
by nuclear reactions initiated by neutrons in
N + 1on ---> 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
Activity of a sample can be used to date the sample. Nuclear Medicine: Imaging Thyroid imaging using Tc-99m 34 35 Food Irradiation
•Food can be irradiated with γ rays from
60Co or 137Cs.
•Irradiated milk has a shelf life of 3 mo.
•USDA has approved irradiation of meats
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