Nuclear Chemistry note s (ver 2): note corrections
Nuclear reactions are NOT normal chemical reactions they can change what the atoms is called,
so in a sense matter is not conserved. But, Energy is; according to the equation E=mC2,
m=mass that goes “missing” due to “mass defect”
Where:
E is the energy (LOTS of it; mega/giga joules not just kilojoules)
C= a constant equal to the speed of light; 3 x 108 m/s
“mass defect” is the odd observation that the whole is actually less than the sum of the
parts. (you must be very careful remember that neutrons actually have a slightly greater mass
than protons and that electrons do have a very, very, very small mass (about 2,000 times less
than protons or neutrons). This means that when a hydrogen-2 isotope (aka deuterium) is
slammed into (fusion) another 21H isotope (deuterium) the resulting helium atom has a mass a
tinny bit less than the mass of these two deuterium atoms. It also means that when Th-230 splits
into lighter isotopes the sum of the masses of all the pieces is slightly less than the original
Thorium isotope and whatever broke it apart.
For our purposes we will continue to think of protons and neutrons as having a mass of 1 a.m.u
(atomic mass unit) and electrons as having a mass of 0 a.m.u.’s
In a Nuclear reaction the element can undergo Transmutation (changing to a new element)
The nuclear line of stability starts out with a one to one ratio of neutrons to protons but by the 6th period is closer
to 2 ½ to 1 ratio. Isotopes not in this stable are can undergo radioactive process to get back to this stable ratio.
Summary of Types of radioactive processes
Alpha: 21887Fr  21485At +
Beta:
14
6C
 147N +
Gamma:
0
0
Positron:
64
29Cu
Neutron:
137
53I
0
4
2He
mass number reduced by 4, charge -2
-1e
atomic number +1
= pure energy
 6428Ni +
 13653I +
Electron Capture: 19579Au +
1
no apparent change; just energy
0
+1e
0n
0
-1e
atomic number decreases by one
mass number decreases by one
 19578Pt
atomic number decreases by one
There is a great variety of damage that can be done by different amounts and types of radiation:
o
Alpha: the nuclei of a helium atom; can be blocked by a paper or dead skin
o
Beta: the electron coming from a nuclei (when a neutron breaks up) can penetrate
skin, is stopped by thin wood (think spark/shock)
o Gamma: goes thru almost everything (x-rays are an example); need several cm of
lead to stop
General review and nuclear reaction balancing practice:
Give the composition of the nucleus of the following isotopes:
a)
136
53I
example:
iodine has 53 protons in the nucleus and (136-53=) 83 neutrons
b) 6428Ni
c)
d)
e)
14
6C
12
6C
230
90Th
Complete the following by writing the correct formula for “?”
a)
 6428Ni + “?”
? = 0+1e; a positron called positron emission. A proton in the
nucleus becomes a neutron and an anti-electron (positron) is emitted. This means that the copper atom
transmutates into a nickel atom.
b)
14
6C
c)
234
90Th
d)
216
84Po
e)
238
92U
 “?” +
f)
24
11Na
 “?” +
g)
32
15P
64
29Cu
 “?” + 0-1e
? = 147N ; this is what happens with carbon 14; it transmutates into
carbon -14. The amount of carbon 14 is thought to be fairly constant. It is formed in the upper
atmosphere by solar radiation and drifts down (as carbon-dioxide) to be used as the building material in
plants so that while a plant is alive it has a “known amount (really a percentage)” of C-14; when the
plant stops growing the amount of carbon 14 starts to decrease (thru beta decay into nitrogen -14); the
longer the plant has been dead the smaller the percentage of carbon 14 present.
 “?” + 42He ; this helium nucleus is also called an alpha particle so Thorium undergoes
alpha decay to form __________; which is also unstable and will under further decay
 “?” +
 “?” +
4
2He
4
2He
0
0
-1e
-1e
; “?” = _______________
; “?” = _______________
; “?” = _______________
; “?” = _______________
Nuclear Reaction Worksheet
Write the following isotopes in the form: azX
Carbon -14 __________
Oxygen-16
__________
Zinc -64 ___________
Carbon -12 __________
Oxygen-18
__________
Zinc -67 ___________
Fill in the missing symbol and name the following reactions:
Alpha() decay , Beta() decay, positron emission, neutron emission, electron capture, gamma() emission,
fission, fusion
Reaction
Name

1
3
1H
2
232
92U
3
144
58Ce
4
65
30Zn
5
40
19K

40
18Ar
6
7
4Be

7
4Be
7
1
0n
235
8
222
86Rn
9
129
53I
10
1
1H
11
239
94Pu
12
15
8O

15
7N
+ ____
13
14
6C

14
7N
+
14
61
28___
15
195
82Pb
+
3
2He

228

0
-1e
+
88Ra
+ ___ + ___ + ___
_______________________
+ ___
_______________________
0
+1e
_______________________
144
59Pr
 _____ +
0
1e
+
236
129
54Xe
_______________________

92U
 ____ +

_______________________
+ ___

92U
_______________________
+ ____ + 3 10n
+
0
-1e

_______________________
0
+1e
_______________________
4
2He
_______________________
_______________________
0
-1e
61
27Co
_______________________
_______________________
+ ____
 ____ +
+ __
55Cs
4
2He
+ 11H  ____ +

141
(very famous)
0
+1e
195
79Au
_______________________
_______________________
(the alchemists dream)
_______________________
A natural transmutation series: Most radioactive decays are a series of steps. Beginning with U-235
and ending up with an isotope of lead. Use the table of steps and emitted particles to identify each element in
the series with its chemical symbol.
Step
1
2
3
4
5
6
7
8
9
10
11
12
Particle
emitted
Alpha
Beta
Alpha
Alpha
Beta
Alpha
Alpha
Alpha
Beta
Alpha
Beta
Stable;
STOP
211
209
MASS NUMBER
207
205
203
201
80
 23190 Th23191 Pa 
isotope of lead?
235
92U
81

82

83

84
85
86
87
88
ATOMIC NUMBER


The stable isotope that is the end product is…… _________________


89
90

91
92
 which
Half Life calculations:
Strontium -90; half life is 20 years
# of half
0
1
lives
Age
0 years
Radioactive
amount
Fraction
remaining
60 years
5
6
100 years
1
½
¼
1/8
1/16
1/32
1/64
1
2
3
4
5
6
40 g
5g
2
3
4
5
6
192 g
1
256 g
1
Estimate the required times
Radioisotope
Half life
Polonium-216
Sodium-54
Radium-226
Bismuth-212
U-238
Chlorine-36
4
160 g
Nitrogen -13; half life is 10 minutes
# of half
0
1
lives
Time
0 minutes
Radioactive
amount
Fraction
remaining
3
320 g
Iodine-131; half life is 8days
# of half
0
lives
Time
0 days
Radioactive
amount
Fraction
remaining
2
Decay time to 1/8 of
original amount
Decay time to 1/32 of
original amount
0.16 seconds
15 hours
1600 years
1 hour
4.5 billion years
400,000 years
1. 100 grams of a radioisotope decays 25 grams in 12 days. Calculate its half-life.
2. 200 grams of a radioisotope decays 25 grams in 90 seconds. Calculate its half-life.
3. 32 grams of a radioisotope decays 2 grams in 40 hours. Calculate its half-life.
Carbon -14 Dating
Carbon-14 undergoes beta decay to Nitrogen-14 exponentially over thousands of years. GRAPH the
following data and connect the points with a smooth curve then answer the questions. Make sure you
include a TITLE, LABELS, UNITS and appropriate increments. Plot Age on horizontal and % on
vertical axis
Age
0
(years)
% of
original 100
14
6C
1.
2.
3.
4.
1000
2000
3000
4000
5000
6000
7000
8000
9000
10,000
89
78.5
70
62
56
48
43
38
34
30
Determine the age of a bone fragment that has 75% of its original Carbon-14
________
Determine the age of a arrow shaft that has 95% of its original Carbon-14
________
Determine the age of some charred wood that has 36% of its original Carbon-14
________
Determine the age of a bone fragment that has 75% of its original Carbon-14
________
5. Determine the % of original Carbon-14 a 1500 year old tree ring would have
________
6. Determine the % of original Carbon-14 a 400 year old manuscript would have ________