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1
Nuclear Chemistry
Proposal: build a
nuclear power plant
in Broome County.
List the pros & cons
2
Nuclear Chemistry
Friend or Fiend
3
The NucleusWhat is in the nucleus?
How big is it vs. the atom?
How was it discovered?
4
Isotope Notation(protons & neutrons in nucleus)
X(p+n)
p C14
6
mass #
atomic #
C -14X -(p+n)
5
Notation: Try It
U238
92Pb -210
How many p, n, and e- ?
What is the nuclear charge of Br?
What is the charge of the
bromide ion?
What is the difference between
mass number and atomic mass?
6
Types of Radiation
Unstable nuclei will change
(or “decay”) by emitting radiation.
b
g
a
+
-unstable
nucleielectric
fieldscreen
7
a Radiation
Some nuclei eject a positive
a (alpha) particle. A piece of
paper can stop an a particle.
Why is it stopped so easily?
2a4
high mass
high charge
What element is a related to?
8
b Radiation
Some nuclei eject a fast
moving electron or beta particle
(b particle).
e-
9
g Radiation
g (gamma) radiation is high energy
light (electromagnetic radiation)
that can easily penetrate wood,
bricks, and human tissue.
g
10
Radiation Damage
Type of
Radiation
Damage to
Human Tissue
a low
b moderate
g high
11
Elementary Particles
1Proton 1p or 1H
1
44Alpha 2He or 2a
00Positron 1e or 1b or b+
0 0Electron -1e or -1b or b-
1Neutron 0n
0Gamma 0g
12
Electron vs. Beta (Identical)
-1e or -1b or b-
From atomic orbit
Ejected from nucleus
00
13
1.Mass number of products &
reactants are equal.
(superscripts balance)
2.Charge of products & reactants
are equal (subscripts balance)
Balancing Nuclear Reactions
14
Balancing Nuclear Reactions
137
55Cs
137
56Ba + X
212
84Po
208
82Pb + X
15
Balancing Nuclear Reactions
78
33As
-1e + X0
14
7N + 0n
14
6C + X
1
16
Try Another!
Write a balanced nuclear
equation for the decay of
Ra-226 to produce an isotope
of radon (Rn) and an alpha
particle.
17
Transmutation
1. Natural Transmutation
2. Artificial Transmutation
(man-made)
Conversion of one
element into another
18
A
Natural TransmutationAn unstable nucleus changes
into another element by emitting
a particle in a process called
“radioactive decay.”
Bparticle and/or
g radiation (light)
19
What Holds a
Nucleus Together?
charge
repulsion
of protons
nucleus
flies apart
“strong
force”
holds nucleus
together
vs
20
Nuclear Stability
Over 1500 isotopes (nuclei) are
known, but only 264 are “stable.”
21
Belt of Stability
20 40 60 80
40 80 120
#p = #n
Number of p
Nu
mb
er
of
n
22
Stable Nuclei
1.Low atomic number: #n = #p
e.g. C-12, N-14, O-16
2.High atomic number: #n > #p
e.g. Pb-206 (82 p & 124 n)
3.All nuclei with atomic
number > 82 are unstable
(too many p & n)
n
p
23
Belt of Stability
20 40 60 80
40 80 120
Number of p
Nu
mb
er
of
nIsotope mass
> PT atomic mass
AIsotope mass
< PT atomic mass
B
b-emission
b+emission
C > Pb
a emission
At. mass on
PT is a guide
to stability
24
Region A
0n 1p1 1
42
19K
42
20Ca + -1e
0
0-1e+ b-
emission
Isotope mass greater than atomic
mass on P.T. results in b- emission
greater than P.T. (39 amu)
25
Region B
111p 0n + 1e
0
37
19K
37
18Ar + 1e
0
Isotope mass less than atomic
mass on P.T. results in b+ emission
b+
emission
less than P.T. (39 amu)
26
Region C
For nuclei past lead (Pb) alpha
emission reduces both n & p.
238
92U
234
90Th + 2a
4
Past Pb on P.T.
27
Nuclear Stability: Summary
Region Emission
Atomic
numbers
1-82
A: too many n
mass # > PT mass
beta
b-
B: too few n
mass # < PT mass
positron
b+
Atomic
number
>82
C: too many p & n
alpha
a
28
Using Table N
Write balanced equations for
the decay of:
N-16
Rn-222
Table N shows the natural
transmutation of several “nuclides.”
29
Predict the Reaction
Write the decay reaction of:
Cu-66 Ti-45
Pu-239 C-14
Check Table N first.
If not on ‘N’, use “rules of stability.”
30
Radioactive Decay Series
Sequence of nuclear reactions
leading to stable isotope.
31
Radioactive Decay Series
parent daughter
Final stable daughter: Pb206
82
e.g.
238
92U
234
90Th + 2a
4
Still not stable
32
Radioactive Half-Life
Half-life (T½): time for one-half
of the radioactive atoms to
decay into products.
Long T½ relatively
stable isotope
You don’t know when an
individual isotope will decay !
33
Half-Life Decay
0 1 2 3 half-lives
100
50
25
0%re
ma
inin
ginitial
1 half-life
2 half-lives
3 half-lives
34
Solving Half-Life Problems
Example: If T½ = 7.2 s and
elapsed time = 28.8 s, then
= 4 half-life periods28.8 s
7.2 s
elapsed time = half-life periodsT½
Half-Life: Loop Method
35
How much of a 50.g sample of
K-42 remains after 37.2 h?
Table N shows half-life is 12.4 h.37.2 h
12.4 h= 3 half-life periods (3 loops)
50. g
6.25 g remains.
1half-life
25 g
2half-life
12.5 g
3half-life
6.25 g
36
Half-Life Problem
You start with 68 g of C-14
•Write a balanced equation
for its decay.
•How long is 3 half-life periods?
•How many grams of C-14
remain after 3 half lives?
37
Half-Life Problem
What percent of I-131will
remain after 40.1 days?
What fraction of I-131will
remain after 24.1 days?
38
Alchemist’s Dream
39
Artificial Transmutation
Rutherford 1919: discovered proton.
14
7N + 2a
17
8O + 1p
4 1
“Bombard” a nucleus with a
particle to form a new element.
2 reactants
= artificial trans.
can’t predict
both products
Alpha injected into nucleus with
particle accelerator.
40
Artificial Transmutation
Chadwick 1932:
discovered the neutron:
Why was detecting the
neutron so difficult?
9
4Be + 2a
12
6C + 0n
4 1
41
Artificial TransmutationAll elements with Z > 92
(transuranium elements) were
produced by transmutation.
Artificial or man-made
238
92U + 0n
239
93Np + -1e
1 0
42
Uses of RadioisotopesRadioactive dating
Radioactive tracers (read p.860)
Medical applications
Nuclear power
43
Radioactive Dating: C-14
C-12 >99% stable
C-14 <1% unstable
After the plant dies,
only C-14 decays.
The ratio of C-14 to C-12
can tell the age since death.
44
Radioactive Dating
Dates living things up to ~40,000 yr
14
6C
14
7N + -1b T½ = 5715 yr
0
Dates rocks billions of years.
238
92U
206
82Pb + 6 -1b + 8 2a
T½ = 4.47 x 109 yr
40
Does this equation balance?
45
Radioactive Dating
46
Cobalt-60, a gamma ray
emitter for treating cancer.
Tc-99 for treatment of cancer.
Medical
Applications
Iodine-131 for treatment of
thyroid cancer.
(injested, so need short T½)
47
Nuclear Power
Fission- splitting heavy nuclei
Fusion- combining
light nuclei
48
Fission & FusionMass of products is less
than mass of reactants.
Mass is lost!!!
energy
produced
missing
mass
speed of
light
3 x 108m/s
E = mc2
49
Nuclear Fission
Used in nuclear
power plants
Splitting a large nucleus
into smaller isotopes,
releasing energy.
50
Nuclear Power PlantU-235, hit by a no, splits into
smaller nuclei & 3 no & energy.
chain reaction
235
92 U+ 0n 90
38Sr+ Xe+ 30n143
5411
no U-235
51
Nuclear Fusion
Small nuclei combine (unite)
to form a larger nucleus and
release energy.
Energy from the sun is
produced by fusion.
Required very high temps.
(40,000,000oC) Why?
52
Solar Fusion
E = mc2
1
1H + 2 -1e
4
2He + energy4 0
Hydrogen nuclei fuse into helium.
53
Detecting Radiation
Your senses cannot detect
radiation.
Geiger counter- b radiation
Scintillation counter- all
types of radiation
Film badge-all types of radiation
54
Reactions:Chemical NuclearAtoms
rearranged
Elements
changed
Involves only
electrons
Involves all
atomic particles
Small DE Large DE
Rate depends
on T, P, etc.
Rate is constant
55
Warm-up
56
•What are the three types of
radiation (names and symbols).
• Which is most and least
damaging radiation to humans?
•How many p+, n, e- in Es-252
Warm-up
57
How many p+, n, e- in titanium-48?
What is the nuclear charge of
this isotope?
Write a balance equation for
carbon-14 emitting a beta particle.
Warm-up
58
Write a balanced equations for
the radioactive decay:
Neon-19
Bromine-81
Neptunium-237
Warm-up
59
Write an equation for the decay of:
technetium-99
silicon-26
californium-252
Use Table N or
compare mass number
vs. atomic mass.
Warm-up
60
235
92U+ X
90
38Sr+ Xe+3 0n
143
541
What is X?
61
Warm-up87.5% of an isotope decays
in 4.8 days.
What is its half-life?
Careful !
Warm-up
62
Write an equation for the decay of
O-19, with a half-life of 29 s.
If you start with 120 g of O-19, how
much remains after 116 s?
How long will it take for a sample of
O-19 to drop to one-eighth of its
original amount?
Warm-up
63
If aluminum-27 is bombarded
with an alpha particle, one of the
products is silicon-30.
•What is this process called?
•Write a balanced equation.
14.0 g of Co-60 remains after 21 yr.
What was the original sample size?
Write an equation for the decay of
Fe-53. What is this process called?