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Unit 14 Ch. 28
Nuclear Chemistry
Unit 14 Ch. 28
Nuclear Chemistry
I. The NucleusI. The NucleusI. The NucleusI. The NucleusI
IV
III
II
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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 = mc2E: energy (J)m: mass defect (kg)c: speed of light
(3.00×108 m/s)
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B. Nuclear Binding Energy
Unstable nuclides are radioactive and undergo radioactive decay.
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UNIT 14 Ch. 28
Nuclear Chemistry
UNIT 14 Ch. 28
Nuclear Chemistry
II. Radioactive II. Radioactive DecayDecay
II. Radioactive II. Radioactive DecayDecay
I
IV
III
II
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He42
A. Types of Radiation
• Alpha particle ()– helium nucleus paper2+
Beta particle (-) electron e0
-11-
leadPositron (+)
positron e01
1+
Gamma () high-energy photon 0
concrete
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B. Nuclear Decay
• Alpha Emission
He Th U 42
23490
23892
parentnuclide
daughternuclide
alphaparticle
Numbers must balance!!
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B. Nuclear Decay
• Beta Emission
e Xe I 0-1
13154
13153
electronPositron Emission
e Ar K 01
3818
3819
positron
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B. Nuclear Decay
• Electron Capture
Pd e Ag 10646
0-1
10647
electronGamma 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
He Th U 42
23490
23892
e Xe I 0-1
13154
13153
e Ar K 01
3818
3819
Pd e Ag 10646
0-1
10647
DECAY SERIES TRANSPARENCY
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C. Half-life
• Half-life (t½)– Time required for half the atoms of a radioactive
nuclide to decay.– Shorter half-life = less stable.
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C. Half-life
nif mm )( 2
1
mf: final massmi: initial massn: # 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
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UNIT 14
Nuclear Chemistry
UNIT 14
Nuclear Chemistry
III. Fission & III. Fission & FusionFusion
III. Fission & III. Fission & FusionFusion
I
IV
III
II
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A. F ission
• splitting a nucleus into two or more smaller nuclei
• 1 g of 235U = 3 tons of coal
U23592
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A. F ission
• chain reaction - self-propagating reaction• critical mass -
mass required to sustain a chain reaction
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B. Fusion• combining of two nuclei to form one nucleus of
larger mass• thermonuclear reaction – requires temp of
40,000,000 K to sustain• 1 g of fusion fuel =
20 tons of coal• occurs naturally in
stars
HH 31
21
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C. Fission vs. Fusion
• 235U is limited• danger of meltdown• toxic waste• thermal pollution
• fuel is abundant• no danger of meltdown• no toxic waste• not yet sustainable
FISSION
FUSION
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UNIT 14
Nuclear Chemistry
UNIT 14
Nuclear Chemistry
IV. ApplicationsIV. ApplicationsIV. ApplicationsIV. ApplicationsI
IV
III
II
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A. Nuclear Power
• Fission Reactors Cooling Tower
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A. Nuclear Power
• Fission Reactors
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A. Nuclear Power
• Fusion Reactors (not yet sustainable)
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A. Nuclear Power
• Fusion Reactors (not yet sustainable)
Tokamak Fusion Test Reactor
Princeton University
National Spherical Torus Experiment
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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
Pu He U 24294
42
23892
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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
Radiation treatment using-rays from cobalt-60.
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E. Nuclear Weapons
• Atomic Bomb– chemical explosion is used to form a critical mass of
235U or 239Pu– fission develops into an uncontrolled chain reaction
• Hydrogen Bomb– chemical explosion fission fusion– fusion increases the fission rate– more powerful than the atomic bomb
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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