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Nuclear Chemistry
• What is radioactivity?
• What are the 3 types of nuclear
radiation?
2
Nuclear Chemistry
• The study of changes that occur in the
nucleus of an ATOM!!!
• Radioactivity - the process in which an
unstable atomic nucleus emits charged
particles and/or energy (also called nuclear
decay)
• During "nuclear decay", an atom of one
element can change into an atom of a
different element.
Chemical vs. Nuclear Reactions
Chemical Reactions
Nuclear Reactions
Occur when bonds Occur when nuclei
are broken
emit particles
and/or rays
Chemical vs. Nuclear Reactions
Chemical Reactions
Nuclear Reactions
Occur when bonds are broken
Occur when nuclei emit particles
and/or rays
Atoms remain
unchanged,
although they may
be rearranged
Atoms often
converted into
atoms of another
element
Chemical vs. Nuclear Reactions
Chemical Reactions
Nuclear Reactions
Occur when bonds are broken
Occur when nuclei emit particles
and/or rays
Atoms remain unchanged, although
they may be rearranged
Atoms often converted into atoms of
another element
Involve only
valence electrons
May involve
protons, neutrons,
and electrons
Chemical vs. Nuclear Reactions
Chemical Reactions
Nuclear Reactions
Occur when bonds are broken
Occur when nuclei emit particles
and/or rays
Atoms remain unchanged, although
they may be rearranged
Atoms often converted into atoms of
another element
Involve only valence electrons
May involve protons, neutrons, and
electrons
Associated with
small energy
changes
Associated with
large energy
changes
Chemical vs. Nuclear Reactions
Chemical Reactions
Nuclear Reactions
Occur when bonds are broken
Occur when nuclei emit particles
and/or rays
Atoms remain unchanged, although
they may be rearranged
Atoms often converted into atoms of
another element
Involve only valence electrons
May involve protons, neutrons, and
electrons
Associated with small energy changes
Associated with large energy changes
Reaction rate
influenced by
temperature, particle
size, concentration,
etc.
Reaction rate is not
influenced by
temperature, particle
size, concentration,
etc.
Radioactivity
• An unstable atomic nucleus
emits a form of radiation
(alpha, beta, or gamma) to
become stable.
• In other words, the nucleus
decays into a different atom.
Radioactivity
• Alpha Particle – Helium
nucleus
• Beta Particle – electron
• Gamma Ray – high-energy
photon
Types of Nuclear Radiation
• Alpha particles
• Beta particles
• Gamma rays
• Nuclear Decay song
Types of Nuclear Radiation
• Alpha particles - positively charged, made up
of 2 protons and 2 neutrons (same as a
helium nucleus)
• Alpha decay - one product is ALWAYS a
Mass # 4 He
Helium nucleus
Atomic # 2
• The mass and atomic numbers of the
reactant must equal the sum of the mass and
atomic numbers of the products
• (ex)
222 Ra
88

4
2
He +
218
86
Rn
Look up element #86
13
14
Beta Particles
• Beta particles – electron emitted by an
unstable nucleus, negatively charged particle
• Beta decay - one product is 0-1e (because of
it’s negative charge, it is assigned an atomic
number of -1)
• (ex) 146C  0-1e + 147N
• (once again, the sums of mass number and
atomic number of the products must equal
the reactant)
• Once you find the atomic number, you look
for the element on your periodic table!!!
Alpha and Beta Decay Animation
• http://library.thinkquest.org/27954/deq
u.htm
Gamma Decay
• Gamma decay- penetrating ray of energy
emitted by an unstable nucleus
• They have no mass and no charge
• Like X-rays and visible light, gamma rays
travel at the speed of light
• During gamma decay, the atomic number and
mass number of the atom remain the same,
but the energy of the nucleus decreases
• X-rays are emitted by electrons outside the
nucleus, while gamma rays are emitted by
the nucleus.
Decay Particles Penetrating Ability
•
alpha particle
– Least penetrating (can be stopped by a sheet of paper or clothing)
•
beta particle
– More penetrating that alpha (pass through paper, but stopped by a thin
sheet of metal
•
gamma ray
– Much more penetrating that alpha and beta (takes several centimeters of
lead or several meters of concrete to stop gamma radiation)
Effects of Nuclear Radiation
• Background radiation – nuclear radiation that occurs
naturally in the environment
– Examples – radioisotopes in air, water, rocks, plants and
animals
• Nuclear radiation can ionize atoms, so it can damage
the cells and tissues of your body
– Bonds holding proteins and DNA may be broken
• Examples
– Alpha particles: radon gas (can be inhaled and causes lung
cancer)
– Beta particles can damage tissues more than alpha particles
– Gamma rays can expose all organs to ionization damage
Detecting Nuclear Radiation
• Geiger counters
• Film badges
Nuclear Chemistry on youtube
• http://www.youtube.com/watch?v=aEB
GE1Nm7vc
Practice on Nuclear Decay:
• Let’s work on p. 1 of your Nuclear
Chemistry packet!
• Homework – p. 2 of packet
29
Half-Life
• Amount of time it takes for
one half of a sample of
radioactive atoms to decay
Medical Applications of Half-Life
Nuclide
Half-Life
Area of Body
I–131
8.1 days
Thyroid
Fe–59
45.1 days
Red Blood Cells
Sr–87
2.8 hours
Bones
Tc–99
6.0 hours
Heart
Na–24
14.8 hours
Circulatory System
Half-Life Calculation #1
• You have 400 mg of a
radioisotope with a half-life
of 5 minutes. How much will
be left after 30 minutes?
To calculate:
• Start with 400 mg.
• The half-life is 5 minutes, so how much will you
have after 5 minutes?
– 200 mg
• Now, how much will you have at the 10 minute
mark? (remember that after 5 minutes, you will
half of what you started with at that particular
time.)
– 100 mg
• Keep going until you have reached 30 minutes!
• You can also use fractions…you try it!
Half-Life Calculation #2
• Suppose you have a 100 mg
sample of Au-191, which has
a half-life of 3.4 hours. How
much will remain after 10.2
hours?
Half-Life Calculation # 3
• Cobalt-60 is a radioactive
isotope used in cancer
treatment. Co-60 has a half-life
of 5 years. If a hospital starts
with a 1000 mg supply, how
many mg will need to be
purchased after 10 years to
replenish the original supply?
Half-Life Calculation # 4
• A radioisotope has a half-life
of 1 hour. If you began with
a 100 g sample of the
element at noon, how much
remains at 3 PM? At 6 PM?
At 10 PM?
Half-Life Calculation # 5
• How many half-lives have
passed if 255 g of Co-60
remain from a sample of
8160 g?
Half-Life Calculation # 6
• Suppose you have a sample
containing 400 nuclei of a
radioisotope. If only 25
nuclei remain after one hour,
what is the half-life of the
isotope?
Half-Life Calculation # 7
• If a radioactive element has
diminished by 7/8 of its
original amount in 30
seconds, what is its half-life?
Answers to Half-Life Calculations
• Half-Life Calculation #1
– 6.25 mg
• Half-Life Calculation #2
– 12.5 mg
• Half-Life Calculation #3
– 750 mg
Answers to Half-Life Calculations
• Half-Life Calculation #4
– 12.5 g, 1.5625 g,
0.09765625 g
• Half-Life Calculation #5
– 5 half-lives
Answers to Half-Life Calculations
• Half-Life Calculation #6
– 15 minutes
• Half-Life Calculation #7
– 10 seconds
Video on Fusion and Fission
• http://www.youtube.com/watch?v=Qliifidcuw
• Another one:
• http://www.bbc.co.uk/schools/gcsebites
ize/science/add_aqa/atoms_radiation/n
uclearact.shtml
Fission and Fusion
• Fission- splitting of
atomic nuclei. Tons
of energy produced
from a small mass
• Fusion- combining
atomic nuclei.
Requires high temp,
stars do this.
Fission vs. Fusion
• Look at my Physical Science notes
under nuclear chemistry
Fission
• NOT a natural process
•
Occurs as a result of neutron bombardment
•
heavy nucleus (mass# > 200) splits into two
similar sized pieces
wide range of nuclei produced
•
•
releases lots of energy b/c smaller nuclei more
stable
•
235U
and
239Pu
most important
Fission
• CONTROLLED:
– Nuclear Power Plant
• UNCONTROLLED:
– In reactor = meltdown!
– Atomic bomb!
Fission and Fusion
Fusion
• nuclei fuse together
• for very light elements, stability increases with increasing mass
#
• energy released when two light nuclei combine to larger, more
stable nucleus
• thermonuclear reaction - occurs only at very high temps
lowest temperature required for fusion: 40,000,000 K
• occurs constantly in sun
• Plasma is an example (atoms have been stripped of their
electrons)
• Fusion
Has it occurred on earth?
Hydrogen bomb
Section 10.4
Comparing and Contrasting
a. is the splitting of a large nucleus
into two smaller fragments
c. is the fusing of two small nuclei
into one larger nucleus
b. is widely used as an alternative
energy source
d. is still being researched and
developed as an alternative
energy source
Fission vs. Fusion
Radiation in our lives
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Background radiation
cosmic rays in atmosphere
radon from granite rock (lung cancer)
Foods
bananas, Brazil nuts
Medical exposure
Dental x-ray
Cancer treatment (Cobalt-60)
Detecting art forgeries
Analyzing gunpowder residue
Agricultural research, diagnose disease
Smoke detectors (Americium-241)
What do we do with Nuclear Waste?
• Bury it underground in a spot that is
geologically stable!!
• SC has a nuclear waste site.
Effects of Radiation Video Clips
• Gamma Radiation gone wrong
• Harmful effects of radiation
• Our radiation environment
• Chernobyl