Transcript Nuclear chemistry

 What
subatomic particles are inside the
nucleus?
 Protons
and neutrons
 Collectively
referred to as nucleons
 In
nuclear chemistry, an atom is referred to
as a nuclide
 Identified by # of protons and neutrons

Radium-228
 228
Ra
88
 Belt
of
stability
 Ratio of
neutrons to
protons
 All nuclei
with atomic
numbers
greater
than 83 are
unstable
 Isotope
that is unstable and thus radioactive
Pierre and Marie Curie
Henri Becquerel
 When
the atomic nucleus of one element is
changed into the nucleus of a different
element


Natural
Artificial
 When
an unstable nucleus decays, it emits
radiation in the form of




Alpha ( ) particles
Beta ( -)particles
Positrons ( +)
Gamma ( ) Rays
Table O
 Alpha
particle is a helium nucleus
 Electron
 Same
mass as an electron but with a positive
charge
38
38
K
Ar
19
18
 High
energy electromagnetic waves emitted
from a nucleus as it changes from an excited
state to a ground state
 ENERGY only (no mass and no charge)
0
0
 Conservation
of mass and charge
 Be able to identify a missing particle in the
equation
 Table
N lists types of radioactive decay for
selected radioisotopes
 What
forms when carbon–14 decays?
 Most=
gamma
 medium= beta
 least-= alpha
Beta
Gamma
Alpha
 Collision
of a charged particle with a target
nucleus
 Neutron
collides with a target nucleus
 Natural-
single nucleus undergoing decay
 Artificial-
2 reactants (fast moving particle
and a target nucleus)
 (t1/2)
time required for half the atoms of a
radioactive nuclide to decay
 Table N
How many milligrams of
Phosphorous-32 will remain after
57.2 days if you start with a 4.0 mg
sample?
Number of
Half-lives
Percent of
material
remaining
Time
Amount of
material
remaining
0
1
0
4.0 mg
1
1/2
14.3 days
2.0 mg
2
1/4
28.6 days
1.0 mg
3
1/8
42.9 days
0.50 mg
4
1/16
57.2 days
0.25 mg
Cr-51 has a half-life of 28 days. (A) What
fraction of a sample of Cr-51 will remain
after 168 days? (B) If a sample of Cr-51 has
an original mass of 52.0g, what mass will
remain after 168 days?
Number of
Half-lives
Percent of
material
remaining
Time
Amount of
material
remaining
0
1
0
52.0g
1
1/2
28
26.0g
2
1/4
56
13.0g
3
1/8
84
6.5g
4
1/16
112
3.25g
5
1/32
140
1.625g
6
1/64
168
0.8125g
 Splitting
of a heavy nucleus to produce
lighter nuclei
 Begins with capture of a neutron by
the nucleus of a heavy element like U235 or Pt-239
 Nucleus produced is unstable and
splits producing large amounts of
energy
Chain
reaction
M
A 238
S
S 236
N 234
U
M 232
B
E
230
R
88
89
90
91
Atomic Number
92
 Fuel:
3% U-235 and 97% U-238
 Moderators: used to slow down neutrons so
they can be captured (heavy water,
beryllium, graphite)
 Control rods: controls reaction by absorbing
neutrons and thus preventing further fissions
(Boron, Cadmium)
 Coolants: remove heat energy produced
(heavy water, liquid sodium)
 Shields: protects personnel from radiation
(steel, lead, concrete)
Hydrogen bomb
 Combining
of light nuclei to form heavier
ones
 Occurs in sun where hydrogen nuclei react in
a series to produce helium nuclei
 In
fission and fusion, the total mass of the
products is less than the total mass of the
reactants
 Mass defect: matter that has been converted
into energy
 E=mc2
 Radioactive
dating (carbon-14)
 Tracers (P-31)
 Industrial applications
 Medical applications (I-31, Co-60, Cs-137,
Tc-99)


Quickly eliminated from body
Short half-lives
Annual Radiation Dose
 Damage
normal cells
 Serious illness and death
 Mutation that can be passed on
 Nuclear accident
 Waste=

Long half-life remains
radioactive for extended periods
of time
1986 Chernobyl (Ukraine)
Cernobyl