Transcript Nuclear Chemistry powerpoint

NUCLEAR CHEMISTRY
Unit 2.5
Introduction to Nuclear Chemistry

Nuclear chemistry is the study of the structure of
and the
they undergo.
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 different
element
Involve valence
electrons
Involve protons,
neutrons, and/or
electrons
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 different
element
Involve valence electrons
Involve protons, neutrons, and/or electrons
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 different
element
Involve valence electrons
Involve protons, neutrons, and/or electrons
Small energy changes
Large energy changes
Reaction rate can be
changed.
Reaction rate cannot be
changed
The Discovery of Radioactivity (1895 –
1898):
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found that invisible rays were
emitted when electrons hit the surface of a
fluorosent screen (discovered x-rays)
Becquerel accidently discovered that
phosphorescent
rock produced spots
on photographic plates
The Discovery of Radioactivity (1895 –
1898):
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isolated the components (
emitting the rays
atoms)
– process by which

atoms give off

particles
– the penetrating rays and
by a radioactive source
The Discovery of Radioactivity (1895 –
1898):
Marie Curie, continued

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identified 2 new elements,
and
on the basis of their radioactivity
These findings
theory of indivisible atoms.
Dalton’s
The Discovery of Radioactivity (1895 –
1898):
– atoms of the same element with
different numbers of

– isotopes of atoms with
unstable nuclei (too many or too few neutrons)

– when unstable
nuclei lose energy by emitting
to
become more
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Alpha radiation
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Composition – Alpha particles, same as helium nuclei
4
Symbol – Helium nuclei, 2He, α
Charge – 2+
Mass (amu) – 4
Approximate energy – 5 MeV
Penetrating power – low (0.05 mm body tissue)
Shielding – paper, clothing
Beta radiation
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Composition – Beta particles, same as an electron
Symbol – e-, 0-1β
Charge – 1Mass (amu) – 1/1837 (practically 0)
Approximate energy – 0.05 – 1 MeV
Penetrating power – moderate (4 mm body tissue)
Shielding – metal foil
Gamma radiation
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Composition – High-energy electromagnetic
radiation
Symbol – ooγ
Charge – 0
Mass (amu) – 0
Approximate energy – 1 MeV
Penetrating power – high (penetrates body easily)
Shielding – lead, concrete
Review of Atomic Structure
Nucleus
Electron Cloud
99.9% of the mass 0.01% of the mass
1/10,000 the size of 9,999 times the size
the atom
of the nucleus
Review of Atomic Structure
Nucleus
Electron Cloud
99.9% of the mass
1/10,000 the size of the atom
0.01% of the mass, 9,999 times the size
of the nucleus
Protons (p+) and
neutrons (n0)
Electrons (e-)
Review of Atomic Structure
Nucleus
Electrons
99.9% of the mass
1/10,000 the size of the atom
0.01% of the mass, 9,999 times the size
of the nucleus
Protons (p+) and neutrons (n0)
Electrons (e-)
Positively charged
Negatively charged
Review of Atomic Structure
Nucleus
Electrons
99.9% of the mass
1/10,000 the size of the atom
0.01% of the mass, 9,999 times the size
of the nucleus
Protons (p+) and neutrons (n0)
Electrons (e-)
Positively charged
Negatively charged
Strong nuclear force Weak electrostatic
(holds the protons
force (between
together)
electrons and nucleus
Chemical Symbols
A chemical symbol looks like…
14
6
C
To find the number of
from the
p+ = e- = atomic #
, subtract the
Nuclear Stability
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Isotope is completely stable if the nucleus will
spontaneously
.
Elements with atomic #s
to
are
.
ratio of protons:neutrons (
)
Example: Carbon – 12 has
protons and
neutrons
Nuclear Stability
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Elements with atomic #s
to
are
.
ratio of protons:neutrons (p+ : n0)
Example: Mercury – 200 has
protons and
neutrons
Nuclear Stability
Elements with atomic #s
and
.
 Examples:
and

are
Alpha Decay
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Alpha decay – emission of an alpha particle ( ),
denoted by the symbol 4
, because an α has 2
2
protons and 2 neutrons, just like the He nucleus.
Charge is
because of the 2
.
Alpha decay causes the
number to
decrease by
and the
number to
decrease by .
determines the
element. All nuclear equations are
.
Alpha Decay
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Example 1: Write the nuclear equation for the
radioactive decay of polonium – 210 by alpha
emission.
Step 4:
1: Determine
2:
3:
Draw the
Write
the arrow.
element
alpha
the other
particle.
that
product
you are
(ensuring
starting with.
everything is balanced).
Mass #
Atomic #
Alpha Decay
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Example 2: Write the nuclear equation for the
radioactive decay of radium – 226 by alpha
emission.
Step 4:
1: Determine
2:
3:
Draw the
Write
the arrow.
element
alpha
the other
particle.
that
product
you are
(ensuring
starting with.
everything is balanced).
Mass #
Atomic #
Beta decay
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Beta decay – emission of a beta particle ( ), a fast
moving
, denoted by the symbol
or -10
. β has insignificant mass ( ) and the
charge is
because it’s an
.
Beta decay causes
change in
number
and causes the
number to increase by .
A neutron is converted to a proton and a beta
particle.
Beta Decay
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Example 1: Write the nuclear equation for the
radioactive decay of carbon – 14 by beta emission.
Step 4:
1: Determine
2:
3:
Draw the
Write
the arrow.
element
beta
the other
particle.
that
product
you are
(ensuring
starting with.
everything is balanced).
Mass #
Atomic #
Beta Decay
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Example 2: Write the nuclear equation for the
radioactive decay of zirconium – 97 by beta
decay.
Step 4:
1: Determine
2:
3:
Draw the
Write
the arrow.
element
beta
the other
particle.
that
product
you are
(ensuring
starting with.
everything is balanced).
Mass #
Atomic #
Gamma decay
Gamma rays – high-energy
radiation, denoted by the symbol
.
 γ has no mass (
) and no charge ( ). Thus, it
causes
change in
or
numbers. Gamma rays almost
accompany alpha and beta radiation. However,
since there is
effect on mass number or atomic
number, they are usually
from nuclear
equations.
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Transmutation

the
of an atom of one
element to an atom of a different element.
Radioactive decay is one way that
this occurs!
Review
Type of
Radioactive
Decay
Alpha
Beta
Gamma
Particle
Emitted
4
2
He
0
-1e
α
β
γ
Change in Change in
Mass #
Atomic #
-4
0
0
-2
+1
0
Half-Life
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is the
required for
of a radioisotope’s nuclei to decay into its products.
For any radioisotope,
# of ½ lives
% Remaining
0
1
2
3
100%
50%
25%
12.5%
4
5
6
6.25%
3.125%
1.5625%
Half-Life
Half-Life
100
90
80
% Remaining
70
60
50
40
30
20
10
0
0
1
2
3
# of Half-Lives
4
5
6
7
Half-Life
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For example, suppose you have 10.0 grams of
strontium – 90, which has a half life of 29 years.
How much will be remaining after x number of
# of ½ lives
Time (Years)
Amount
years?
Remaining (g)
You can use a table:
0
1
2
3
4
0
29
58
87
116
10
5
2.5
1.25
0.625
Half-Life
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Or an equation!
Half-Life
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Example 1: 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
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Example 2: 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
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Example 3: 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
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Example 4: 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
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Example 5: 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 Reactions
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Characteristics:
Isotopes of one element are
isotopes of another element
Contents of the
amounts of
into
change
are released
Types of Nuclear Reactions
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decay – alpha and beta
particles and gamma ray emission
Nuclear
- emission of a
or
Nuclear Fission
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of a nucleus
- Very heavy nucleus is split into
approximately
fragments
reaction releases several neutrons
which
more nuclei
- If controlled, energy is released
(like in
) Reaction
control depends on reducing the
of the
neutrons (increases the reaction rate) and
extra neutrons (
creases the
reaction rate).
Nuclear Fission
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- 1st controlled nuclear reaction in December 1942.
1st uncontrolled nuclear explosion occurred July
1945.
- Examples – atomic bomb, current nuclear power
plants
Nuclear Fission
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Disadvantages
 Produces
high level radioactive waste that must be
stored for 10,000’s of years.
 Meltdown causes disasters like in Japan and Chernobyl.
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Advantages
 Zero
air pollution
 Not a fossil fuel so doesn’t contribute to climate change
Nuclear Fusion
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- Fusion: Combining of two nuclei
- Two light nuclei combine to form a single heavier
nucleus
- Does not occur under standard conditions (positive
nuclei repel each other)
- Advantages compared to fission – No radioactive
waste, inexpensive
,
- Disadvantages - requires large amount of energy
to start, difficult to control.
- Examples – energy output of stars, hydrogen
bomb, future nuclear power plants
Uses of Radiation
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Radioactive dating: Carbon–14 used to determine
the age of an object that was once alive.
Detection of diseases: Iodine–131 used to detect
thyroid problems, technetium–99 used to detect
cancerous tumors and brain disorders, phosphorus –
32 used to detect stomach cancer.
Treatment of some malignant tumors (cobalt–60
and cesium–137) cancer cells are more sensitive to
radiation than normal, healthy cells
Uses of Radiation
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X-rays
Radioactive tracers: used in research to tag
chemicals to follow in living organisms
Everyday items: thorium–232 used in lantern
mantels, plutonium–238 used in long-lasting
batteries for space, and americium–241 in smoke
detectors.