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NUCLEAR CHEMISTRY
Unit 15
Introduction to Nuclear Chemistry
Nuclear chemistry is the study of the structure of
atomic nuclei and the changes they undergo.
Characteristics of nuclear reactions:
Isotopes of one element are changed into isotopes of
another element
Contents of the nucleus change
Large amounts of energy are released
Chemical vs. Nuclear Reactions
Chemical Reactions Nuclear Reactions
Bonds are broken Nuclei emit particles
and/or rays
Chemical vs. Nuclear Reactions
Chemical Reactions Nuclear Reactions
Bonds are broken Nuclei emit particles and/or rays
Atoms are
rearranged
Atoms changed into
atoms of another
element
Chemical vs. Nuclear Reactions
Chemical Reactions Nuclear Reactions
Bonds are broken Nuclei emit particles and/or rays
Atoms may be rearranged Atoms changed to atoms of a different
element
Involve valence
electrons from
electron cloud
Involve protons,
neutrons, and/or
electrons from
nucleus
Chemical vs. Nuclear Reactions
Chemical Reactions Nuclear Reactions
Bonds are broken Nuclei emit particles and/or rays
Atoms are rearranged Atoms change into atoms of a different
element
Involve valence electrons from electron
cloud
Involve protons, neutrons, and/or electrons
from nucleus
Small energy
changes
Large energy
changes
Chemical vs. Nuclear Reactions
Chemical Reactions Nuclear Reactions
Bonds are broken Nuclei emit particles and/or rays
Atoms are rearranged Atoms change into atoms of a different
element
Involve valence electrons from electron
cloud
Involve protons, neutrons, and/or electrons
from nucleus
Small energy changes Large energy changes
Radioactivity
Radioactivity– process by which atoms give off rays
or particles
Radiation– the penetrating rays and particles
emitted by a radioactive source
The Discovery of Radioactivity (1895 –
1898):
Roentgen found that invisible rays were emitted when electrons hit the surface of a fluorescent screen (discovered x-rays)
Becquerel accidently discovered that phosphorescent uranium rock produced spots on photographic plates (discovered radioactivity)
Marie and Pierre Curie:
isolated the components emitting the rays (uranium atoms)
identified 2 new elements, polonium and radium on the basis of their radioactivity
These findings contradicted Dalton’s theory of indivisible atoms.
Review of Atomic Structure
Nucleus Electron Cloud
Majority of the mass
of the atom (99.9%)
None of the volume
of the atom (0.01%)
None of the mass of
the atom (0.01%)
Majority of the
volume of the atom
(9,999 times the size
of the nucleus)
Review of Atomic Structure
Nucleus Electron Cloud
Majority of the mass of the atom (99.9%)
None of the volume of the atom (0.01%)
None of the mass of the atom (0.01%)
Majority of the volume of the atom (9,999
times the size of the nucleus)
Protons (p+) and
neutrons (n0)
Electrons (e-)
Review of Atomic Structure
Nucleus Electron cloud
Majority of the mass of the atom (99.9%)
None of the volume of the atom (0.01%)
None of the mass of the atom (0.01%)
Majority of the volume of the atom (9,999
times the size of the nucleus)
Protons (p+) and neutrons (n0) Electrons (e-)
Positively charged Negatively charged
Review of Atomic Structure
Nucleus Electron cloud
Majority of the mass of the atom (99.9%)
None of the volume of the atom (0.01%)
None of the mass of the atom (0.01%)
Majority of the volume of the atom (9,999
times the size of the nucleus)
Protons (p+) and neutrons (n0) Electrons (e-)
Positively charged Negatively charged
Strong nuclear force
holds the protons
together
Weak electrostatic
force between
negatively charged
electrons and positively
charged nucleus
nucleons – particles found in the nucleus
Neutrons and protons
The nuclear symbol consists of three parts:
Element symbol
atomic number (Z) – number of protons in the
nucleus
mass number (A) – sum of the number of protons
and neutrons
Also written as the element name dash (-) mass
number (example: Carbon- 12)
nuclide – each unique atom
Ion- an atom with a charge
A Review of Atomic Terms
Radioactivity:
Isotopes– atoms of the same element with different
numbers of neutrons
Radioisotopes– isotopes of atoms with unstable
nuclei (too many or too few neutrons)
Radioactive decay– when unstable nuclei lose
energy by emitting radiation to become more
stable
This is a spontaneous reaction (happens on its own)
Nuclear Stability
Generally elements with atomic #s 1 to 20 are very
stable.
Isotope is completely stable if the nucleus will not
spontaneously decompose.
1:1ratio of protons : neutrons (p+; n0)
Example: Carbon – 12 has 6 protons and 6 neutrons
Nuclear Stability
Generally elements with atomic #s 21to 83 are
marginally stable.
1:1.5 ratio of protons:neutrons (p+:n0)
Example: Mercury – 200 has 80 protons and 120
neutrons
Nuclear Stability
Generally elements with atomic #s > 83 are
unstable and radioactive.
Examples: Uranium and Plutonium
Nuclear Reactions
Types of Nuclear Reactions:
Radioactive decay – alpha and beta particles and
gamma ray emission
Nuclear disintegration - emission of a proton or neutron
Transmutation the conversion of an atom of one
element to an atom of a different element.
Usually occurs by radioactive decay
Nuclear Equation
Nuclear equation – shows the radioactive
decomposition of an element
Alpha radiation
Composition – Alpha particles, same as a helium nuclei
Symbol – Helium nuclei, He, α
Charge – 2+
Deflected towards a negatively charged plate
Mass – 4 amu
Approximate energy – 5.0 MeV
Penetrating power – low (0.05 mm body tissue)
Shielding – paper, clothing
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Alpha Decay
Example 1: Write the nuclear equation for the radioactive decay of polonium – 210 by alpha emission.
Mass #
Atomic #
Step 1: Write the nuclear symbol for the element that you are
starting with followed by the yields symbol.
Step 2: Write the alpha particle as a product
Step 3: Determine the other product using atomic #.
Step 4: Determine mass and ensure everything is balanced.(Net effect is loss of 4 in mass number and loss of 2 in atomic number.)
Alpha Decay
Example 2: Write the nuclear equation for the
radioactive decay of radium – 226 by alpha
emission.
Beta radiation
Composition – Beta particles, same as a fast moving electron
A neutron is converted to a proton and a beta particle.
Symbol – −10𝑒, 0-1β
Charge – 1-
Deflected towards a positively charged plate
Mass (amu) – 1/1837 (practically 0)
Approximate energy – 0.05 – 1 MeV
Penetrating power – moderate (4 mm body tissue)
Shielding – metal foil
Beta Decay
Example 3: Write the nuclear equation for the
radioactive decay of carbon – 14 by beta emission.
Steps: same steps as alpha equations except use a
beta particle(Net effect is no change in mass and addition of 1 in
atomic number.)
Beta Decay
Example 4: Write the nuclear equation for the
radioactive decay of zirconium – 97 by beta
decay.
Gamma radiation
Composition – gamma ray, High-energy electromagnetic radiation or high energy photon
Usually accompanied by alpha and beta radiation
Symbol – ooγ or γ
Charge – 0
Mass (amu) – 0
Approximate energy – 1 MeV
Penetrating power – high (penetrates body easily)
Shielding – lead, concrete, water
Gamma Decay
Example 5: Write the nuclear equation for the
radioactive decay of uranium – 238 by gamma
decay accompanied with alpha decay.
Steps: include alpha and/or beta, and gamma decay
Radioactive Decay
Review
Type of
Radioactive
Decay
Particle
Emitted
Change in
Mass #
Change in
Atomic #
Alpha α He -4 -2
Beta β e 0 +1
Gamma γ 0 (plus
alpha
and/or
beta
decay)
0 (plus
alpha
and/or
beta
decay)
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0-1
Radioactive Decay
Decay series:
when a substance
undergoes a series
of nuclear decay
Half-Life
Half-life is the time required for half of a
radioisotope’s nuclei to decay into its products.
For any radioisotope,
# of ½ lives % Remaining
0 100%
1 50%
2 25%
3 12.5%
4 6.25%
5 3.125%
6 1.5625%
Half-Life
0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5 6 7
% R
em
ain
ing
# of Half-Lives
Half-Life
Half-Life
Example 6: suppose you have 10.0 grams of
strontium – 90, which has a half life of 29 years.
How much will be remaining after 116 number of
years?
You can use a table:
# of ½ lives Time (Years) Amount
Remaining (g)
0 0 10
1 29 5
2 58 2.5
3 87 1.25
4 116 0.625
Half-Life
Or an equation!
Half-Life
Example 7: If gallium – 68 has a half-life of 68.3
minutes, how much of a 160.0 mg sample is left
after 1 half life? ________
2 half lives? __________ 3 half lives? __________
Half-Life
Example 8: Cobalt – 60, with a half-life of 5 years,
is used in cancer radiation treatments. If a hospital
purchases a supply of 30.0 g, how much would be
left after 15 years? ______________
Half-Life
Example 9: Iron-59 is used in medicine to diagnose
blood circulation disorders. The half-life of iron-59
is 44.5 days. How much of a 2.000 mg sample will
remain after 133.5 days? ______________
Half-Life
Example 10: The half-life of polonium-218 is 3.0
minutes. If you start with 20.0 g, how long will it
take before only 1.25 g remains? ______________
Half-Life
Example 11: A sample initially contains 150.0 mg
of radon-222. After 11.4 days, the sample
contains 18.75 mg of radon-222. Calculate the
half-life.
Nuclear Fission
Nuclear Fission- splitting of a nucleus
Releases a lot of energy
Chain reactions occur
Produces radioactive waste
Usually fueled by Uranium
Example: atomic bomb, nuclear reactors, nuclear
power plants
Fission
Nuclear Fusion
Nuclear Fusion- combining of two or more nuclei
Two light nuclei combine to form a single heavier nucleus
Does not occur under standard conditions
Releases a lot of energy (more than fission)
Not radioactive
Can cause chain reactions
Usually fueled by isotopes of hydrogen
Example: energy output of stars (and the sun) and
hydrogen bomb (more powerful than atomic bombs)
Fusion
Advantages and Disadvantages
Advantages
Fission Fusion
• Zero air pollution
• Not a fossil fuel so doesn’t contribute to
climate change
• Able to be controlled
• No radioactive waste
• Inexpensive
Disadvantages
Fission Fusion
• Produces high level radioactive waste
that must be stored for 10,000’s of
years.
• Meltdown causes disasters like in Japan
and Chernobyl.
• Requires large amount of energy to
start
• Difficult to control
Uses of Radiation
Radioactive dating
Detection of diseases
Treatment of some malignant tumors
X-rays
Radioactive tracers
Everyday items: thorium–232 used in lantern mantels, plutonium–238 used in long-lasting batteries for space, and americium–241 in smoke detectors.