Transcript Nuclear Chemistry powerpoint

NUCLEAR CHEMISTRY
Unit 16
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
Occur when bonds
are broken
Occur when nuclei
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
Atoms often
unchanged, although converted into atoms
they may be
of another element
rearranged
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 May involve protons,
electrons
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 Associated with
energy changes
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.
The Discovery of Radioactivity (1895 –
1898):
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found that invisible rays were
emitted when electrons bombarded the surface of
certain materials.
Becquerel accidently discovered that
phosphorescent
salts produced
spontaneous emissions that darkened photographic
plates
The Discovery of Radioactivity (1895 –
1898):
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isolated the components (
emitting the rays
atoms)
– process by which

particles give off

particles
– the penetrating rays and
by a radioactive source
The Discovery of Radioactivity (1895 –
1898):
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
identified 2 new elements,
and
on the basis of their radioactivity
These findings
Dalton’s
theory of indivisible atoms.
The Discovery of Radioactivity (1895 –
1898):
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– atoms of the
element
with different numbers of
– isotopes of atoms with
nuclei (too
/
neutrons)
– when unstable
nuclei
energy by emitting
to attain more
atomic
configurations (
process)
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-, β
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 – γ
Charge – 0
Mass (amu) – 0
Approximate energy – 1 MeV
Penetrating power – high (penetrates body easily)
Shielding – lead, concrete
Review of Atomic Structure
Nucleus
Electrons
99.9% of the mass 0.01% of the mass
1/10,000 the size of
the atom
Review of Atomic Structure
Nucleus
Electrons
99.9% of the mass
1/10,000 the size of the atom
0.01% of the mass
Composed of
protons (p+) and
neutrons (n0)
Composed of
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
Composed of protons (p+) and neutrons
(n0)
Composed of 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
Composed of protons (p+) and neutrons
(n0)
Composed of electrons (e-)
Positively charged
Negatively charged
Strong nuclear force Weak electrostatic
(holds the nucleus
force (because they
together)
are charged
negatively
Chemical Symbols

A chemical symbol looks like…
14
6
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C
To find the number of
from the
, 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

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
and causes the
change in
number
number to increase by .
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 one atom of one
element to an atom of a different element
(
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
100%
50%
2
3
4
25%
12.5%
6.25%
5
6
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 Fusion
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of a nuclei
nuclei combine to form a
- Two
heavier nucleus
- Does not occur under standard conditions (
- Advantages compared to fission -
repels )
,
- Disadvantages - requires
amount of
energy to
, difficult to
- Examples – energy output of stars, hydrogen bomb,
future nuclear power plants
Uses of Radiation
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Radioactive _______________ - Carbon - ____ used
to determine the ________ of an object that was once
alive.
___________________________ of diseases – Iodine
– 131 used to detect _________________ problems,
technetium – 99 used to detect ___________ tumors
and ____________ disorders, phosphorus – 32 used to
detect __________ cancer.
Treatment of some _______________________ (cobalt
– 60 and cesium – 137) – cancer cells are more
________________________ to radiation than normal,
healthy cells
Uses of Radiation
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X-rays
Radioactive ________________ (used in research
to _______ chemicals)
Everyday items – thorium – 232 used in
______________________, plutonium – 238 used
in _______________________, and americium –
241 in ___________________________________