Transcript Nuclear Chemistry powerpoint

NUCLEAR CHEMISTRY
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):


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
Antoine Henri Becquierel
Radioactive decay
Discovered by Antoine Henri Becquerel in 1896
He saw that photographic plates developed
bright spots when exposed to uranium metals
Radioactive Decay – nucleus decays
spontaneously giving off an energetic
particle
The Discovery of Radioactivity (1895 –
1898):

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):


identified 2 new elements,
and
on the basis of their radioactivity
These findings
Dalton’s
theory of indivisible atoms.
Marie Sklodowska Curie with her
daughter, Irene.
The Discovery of Radioactivity (1895 –
1898):



– 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







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







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







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
Ionizing power and penetrating
power: an analogy.
Types of radioactive decay





alpha particle emission
beta emission
positron emission
electron capture
gamma emission
Alpha emission
Beta Particle emisson
1
0
n p  e
1
1
0
1
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
Chemical Symbols

A chemical symbol looks like…
14
6

C
To find the number of
from the
, subtract the
Half-Life


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


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

Or an equation!
Half-Life

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

Example 2: 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? ______________
Nuclear Fission




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


- 1st controlled nuclear reaction in December 1942.
1st uncontrolled nuclear explosion occurred July
1945.
- Examples – atomic bomb, current nuclear power
plants
© 2003 John Wiley and Sons Publishers
Courtesy David Bartruff/Corbis Images
Cooling towers of a nuclear power plant.
Construction of a tunnel that will be used for burial of radioactive wastes deep within Yucca
Mountain, Nevada.
Disposal of radioactive wastes by burial in a
shallow pit.
Nuclear Fusion






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
Applications
Medicine
Chemotherapy
Power pacemakers
Diagnostic tracers
Agriculture
Irradiate food
Pesticide
Energy
Fission
Fusion
X-ray examination of luggage at a
security station.
An image of a thyroid gland obtained
through the use of radioactive iodine
Images of human lungs obtained from
a γ-ray scan.
A cancer patient receiving radiation
therapy.