Transcript
Nuclear Chemistry
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XAZ
Mass Number
Atomic NumberElement Symbol
Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
A
Z
1p1
1H1or
proton1n0
neutron0e-1
0b-1or
electron0e+1
0b+1or
positron4He2
4a2or
a particle
1
1
1
0
0
-1
0
+1
4
2
23.1
Diagram showing penetrating ability
www.epa.gov
Balancing Nuclear Equations
1. Conserve mass number (A).
The sum of protons plus neutrons in the products must equal
the sum of protons plus neutrons in the reactants.
1n0U23592 + Cs
13855 Rb
9637
1n0+ + 2
235 + 1 = 138 + 96 + 2x1
2. Conserve atomic number (Z) or nuclear charge.
The sum of nuclear charges in the products must equal the
sum of nuclear charges in the reactants.
1n0U23592 + Cs
13855 Rb
9637
1n0+ + 2
92 + 0 = 55 + 37 + 2x023.1
212Po decays by alpha emission. Write the balanced
nuclear equation for the decay of 212Po.
4He2
4a2oralpha particle -
212Po 4He + AX84 2 Z
212 = 4 + A A = 208
84 = 2 + Z Z = 82
212Po 4He + 208Pb84 2 82
23.1
23.1
Nuclear Stability and Radioactive Decay
Beta decay
14C 14N + 0b + n6 7 -140K 40Ca + 0b + n19 20 -1
1n 1p + 0b + n0 1 -1
Decrease # of neutrons by 1
Increase # of protons by 1
Positron decay
11C 11B + 0b + n6 5 +138K 38Ar + 0b + n19 18 +1
1p 1n + 0b + n1 0 +1
Increase # of neutrons by 1
Decrease # of protons by 1
n and n have A = 0 and Z = 023.2
Electron capture decay
Increase # of neutrons by 1
Decrease # of protons by 1
Nuclear Stability and Radioactive Decay
37Ar + 0e 37Cl + n18 17-1
55Fe + 0e 55Mn + n26 25-1
1p + 0e 1n + n1 0-1
Alpha decay
Decrease # of neutrons by 2
Decrease # of protons by 2212Po 4He + 208Pb84 2 82
Spontaneous fission
252Cf 2125In + 21n98 49 023.2
n/p too large
beta decay
X
n/p too small
positron decay or electron capture
Y
23.2
Nuclear Stability
Certain numbers of neutrons and protons are extra stable
n or p = 2, 8, 20, 50, 82 and 126
Like extra stable numbers of electrons in noble gases (e- = 2, 10, 18, 36, 54 and 86)
Nuclei with even numbers of both protons and neutrons are more stable than those with odd numbers of neutron and protons
All isotopes of the elements with atomic numbers higher than 83 are radioactive
All isotopes of Tc and Pm are radioactive
23.2
Nuclear binding energy (BE) is the energy required to break
up a nucleus into its component protons and neutrons.
BE + 19F 91p + 101n9 1 0
BE = 9 x (p mass) + 10 x (n mass) 19F mass
E = mc2
BE (amu) = 9 x 1.007825 + 10 x 1.008665 18.9984
BE = 0.1587 amu 1 amu = 1.49 x 10-10 J
BE = 2.37 x 10-11J
binding energy per nucleon = binding energy
number of nucleons
= 2.37 x 10-11 J
19 nucleons= 1.25 x 10-12 J
23.2
Nuclear binding energy per nucleon vs Mass number
nuclear stability
23.2
nuclear binding energy
nucleon
Kinetics of Radioactive Decay
N daughter
rate = -DN
Dtrate = lN
DN
Dt= lN-
N = N0exp(-lt) lnN = lnN0 - lt
N = the number of atoms at time t
N0 = the number of atoms at time t = 0
l is the decay constant
ln2=
tl
23.3
Kinetics of Radioactive Decay
[N] = [N]0exp(-lt) ln[N] = ln[N]0 - lt
[N]
ln [
N]
23.3
Radiocarbon Dating
14N + 1n 14C + 1H7 160
14C 14N + 0b + n6 7 -1 t = 5730 years
Uranium-238 Dating
238U 206Pb + 8 4a + 6 0b92 -182 2 t = 4.51 x 109 years
23.3
Nuclear Transmutation
Cyclotron Particle Accelerator
14N + 4a 17O + 1p7 2 8 1
27Al + 4a 30P + 1n13 2 15 0
14N + 1p 11C + 4a7 1 6 2
23.4
Nuclear Transmutation
23.4
Nuclear Fission
23.5
235U + 1n 90Sr + 143Xe + 31n + Energy92 54380 0
Energy = [mass 235U + mass n (mass 90Sr + mass 143Xe + 3 x mass n )] x c2
Energy = 3.3 x 10-11J per 235U
= 2.0 x 1013 J per mole 235U
Combustion of 1 ton of coal = 5 x 107 J
Nuclear Fission
23.5
235U + 1n 90Sr + 143Xe + 31n + Energy92 54380 0
Representative fission reaction
Nuclear Fission
23.5
Nuclear chain reaction is a self-sustaining sequence of
nuclear fission reactions.
The minimum mass of fissionable material required to
generate a self-sustaining nuclear chain reaction is the
critical mass.
Non-critical
Critical
Schematic Diagram of a Nuclear Reactor
23.5
Annual Waste Production
23.5
35,000 tons SO2
4.5 x 106 tons CO2
1,000 MW coal-fired
power plant
3.5 x 106
ft3 ash
1,000 MW nuclear
power plant
70 ft3
vitrified
waste
Nuclear Fission
23.5
Nuclear Fission
Hazards of the
radioactivities in spent
fuel compared to
uranium ore
From Science, Society and Americas Nuclear Waste, DOE/RW-0361 TG
Chemistry In Action: Natures Own Fission Reactor
Natural Uranium
0.7202 % U-235 99.2798% U-238
Measured at Oklo
0.7171 % U-235
23.6
Nuclear Fusion
2H + 2H 3H + 1H1 1 1 1
Fusion Reaction Energy Released
2H + 3H 4He + 1n1 1 2 0
6Li + 2H 2 4He3 1 2
6.3 x 10-13 J
2.8 x 10-12 J
3.6 x 10-12 J
Tokamak magnetic
plasma
confinement
23.7
Radioisotopes in Medicine
1 out of every 3 hospital patients will undergo a nuclear medicine procedure
24Na, t = 14.8 hr, b emitter, blood-flow tracer
131I, t = 14.8 hr, b emitter, thyroid gland activity
123I, t = 13.3 hr, g-ray emitter, brain imaging
18F, t = 1.8 hr, b+ emitter, positron emission tomography
99mTc, t = 6 hr, g-ray emitter, imaging agent
Brain images
with 123I-labeled
compound
23.7
Radioisotopes in Medicine
98Mo + 1n 99Mo42 0 42
235U + 1n 99Mo + other fission products92 0 42
99mTc 99Tc + g-ray43 43
99Mo 99mTc + 0b + n42 43 -1
Research production of 99Mo
Commercial production of 99Mo
t = 66 hours
t = 6 hours
Bone Scan with 99mTc
Geiger-Mller Counter
23.7
23.8
Biological Effects of Radiation
Radiation absorbed dose (rad)
1 rad = 1 x 10-5 J/g of material
Roentgen equivalent for man (rem)
1 rem = 1 rad x Q Quality Factor
g-ray = 1
b = 1
a = 20
Chemistry In Action: Food Irradiation
Dosage Effect
Up to 100 kilorad
Inhibits sprouting of potatoes, onions, garlics.
Inactivates trichinae in pork. Kills or prevents insects
from reproducing in grains, fruits, and vegetables.
100 1000 kilorads Delays spoilage of meat poultry and fish. Reduces
salmonella. Extends shelf life of some fruit.
1000 to 10,000 kiloradsSterilizes meat, poultry and fish. Kills insects and
microorganisms in spices and seasoning.
Half-lifesThe rate at which a particular radioisotope decays is
described by its half-life.
The half-life is defined as the time that it takes for
one half of a sample of a radioactive element to
decay into another element.
The half-life of a radioisotope is dependent only on
what the radioisotope is.
Table N provides us
with a list of various
nuclides, their decay
modes, and their half-
lifes.
Using Table N, what is
the decay mode and
half-life for Radium-
226?
Using Table N
Table N indicates that Radium-226 undergoes alpha
decay.
Based on this we can write a balanced nuclear equation to
represent this reaction:
This tells us that for every atom of Radium that
decays an atom of Radon is produced.
Using Half-lifeTable N also tells us that Radium-226 has a half-life of
1600 years.
Starting with a 100g
sample, after 1 half-
life (or 1600 years),
50g remain.
After another 1600
years, half of the
50g will remain
(25g).
Carbon-14 Dating
The age of objects that were once alive can be
determined by using the C-14 dating test. In this test,
scientists determine how much C-14 is left in a sample
and from this determine the age of the object.
From Table N we can determine that C-14 undergoes
b decay:
Where does the Carbon-14 come
from?
C-14 is created in the
atmosphere by
cosmic rays.
It becomes part of living
things through
photosynthesis and the
food chain.
When the plant or
animal dies, the C-14
begins to decay.
Using C-14 to Age ObjectsBy comparing the amount of C-14 left in a sample to the amount that
was present when it was alive, and using the half-life of 5700 years
(Table N), one can determine the age of a sample.
Uranium-238 Series
The Uranium-238 Decay Series is used to determine the age of
rocks.
In this series, the
ratio of the U-
238 to the Pb-
206 is used to
determine the
age of the rock.
Parent-daughter Relationship
Aging moon rocks
NASA astronauts have retrieved
842 pounds (382 kg) of moon rocks
(in many missions), which have
been closely studied. The
composition of the moon rocks is
very similar to that of Earth rocks.
Using radioisotope dating, it has
been found that moon rocks are
about 4.3 billion years old.
Sample Half-life Problem 1
A 10 gram of sample of Iodine-131undergoes b decay, what
will be the mass of iodine remaining after 24 days?
From Table N, the life of iodine is determined to be
approximately 8 days.
That means that 24 days is equivalent to 3 half-lifes.
The decay of 10 grams of I-131 would produce:
1.25 grams of I-131 would remain after 24
days.
Sample Half-life Problem 2A sample of a piece of wood is analyzed by C-14 dating. The
percent of C-14 is found to be 25% of what the original C-14
concentration was. What is the age of the sample?
First, lets analyze how many half-lives have taken place.
Two half-lives have gone by while the sample decayed from
the original C-14 concentration to 25% of that concentration.
Based on Table N, the half-life of C-14 is 5730 years,
so
Your turn!
On a sheet of paper, answer the following questions
from your textbook. Indicate how you arrived at your
answer and turn in your work for a homework/quiz
grade.
Page 670
Questions 34 (a and b), 36, 37, 38, 41, 42.
Page 671
Questions 50, 58, 59
The End
This is the end of the first slide show on
nuclear reactions. You may continue
learning about nuclear reactions by viewing
the second show:
Nuclear Chemistry:
Fission and Fusion
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