For Chemistry 150

2. Radioactivity
Spontaneous emission of particles and or radiation.
(name invented by Marie Curie for a
discovery of Henri Becquerel 1896)
•“Rays” of three types are produced by the decay, or
breakdown, of radioactive substances
1. Alpha rays ( α ) – consist of positively helium nuclei and thus are deflected
in an external magnetic and electric fields.
2. Beta rays ( β ) – are electrons and thus are deflected in an external
magnetic and electric fields.
3. Gamma rays ( γ ) – are “light” (electromagnetic radiation) and thus are not
affected by an external electric field or magnetic field

3. –
α Lead block
γ
β
+
Radioactive substance

4. –
Lead block
+

5. –
α Lead block
+
Radioactive substance

6. –
Lead block
β
+
Radioactive substance

7. –
Lead block
γ
+
Radioactive substance

8. –
α Lead block
γ
β
+
Radioactive substance

10. Penetrating Ability

11. Stability
of Nuclei
• Out of > 300 stable isotopes:
N Even Odd
Z
Even 157 52 31
P
15
Odd 50 5
19
F
9
2
1 H, 63Li, 105B, 147N, 18073Ta

12. Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
Mass Number A
ZX
Element Symbol
Atomic Number
proton neutron electron positron α particle
1
1
p or 1H
1
0n
1 0
-1 e or -1β
0 0
+1 e or +1β
0 4
2 He or 2α
4
A 1 1 0 0 4
Z 1 0 -1 +1 2
23.1

13. 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.
235 138 96
92 U + 0n
1
55 Cs + 37 Rb + 2 0n
1
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.
235 138 96
92 U + 0n
1
55 Cs + 37 Rb + 2 0n
1
92 + 0 = 55 + 37 + 2x0
23.1

14. Po decays by alpha emission. Write the balanced
212
nuclear equation for the decay of 212Po.
alpha particle - 2He or 2α
4 4
84Po He + AX
212 4
2 Z
212 = 4 + A A = 208
84 = 2 + Z Z = 82
84 Po 2He + 208Pb
212 4
82
23.1

15. 23.1

16. I. Nuclear Stability and Radioactive Decay

17. n/p too large
beta decay
X
Y
n/p too small
positron decay or electron capture
23.2

19. Stability
of Nuclei
• Out of > 300 stable isotopes:
N Even Odd
Z
Even 157 52 31
P
15
Odd 50 5
19
F
9
2
1 H, 63Li, 105B, 147N, 18073Ta

21. Predicting the mode of decay
1. High n/p ratio (too many neutrons; lie above band
of stability) --- undergoes beta decay
2. Low n/p ratio (neutron poor; lie below band of
stability) --- positron decay or electron capture
3. Heavy nuclides ( Z > 83) --- alpha decay

22. II. Nuclear Transmutations
•Nuclear reactions that are induced in a way that nucleus is struck
by a neutron or by another nucleus (nuclear bombardment)
a.Positive ion bombardment
- alpha particle is the most commonly used positive ion
- uses accelerators
Examples:
7 N + 2 He → 8 O + 1H
14 4 17 1
9
4 Be + 42 He → 126 C + 10n
b.Neutron bombardment
- neutron is bombarded to a nucleus to form a new nucleus
- most commonly used in the transmutation to form
synthetic isotopes because neutron are neutral, they are not
repelled by nucleus
Example:
26 Fe + 0 n → 26 Fe → 27 Co + -1 e
58 1 59 59 0

23. Transuranium elements
-Element with atomic numbers above 92
-Produced using artificial transmutations, either
by:
a. alpha bombardment
b. neutron bombardment
c. bombardment from other nuclei
Examples:
239 242
94 Pu + 2He + 1n
4
a. 96 Cm 0
238 239
b. 92 U + 0n
1
92 U
239 239
94 Pu+ -1 e
0
93 Np + 0
-1 e
238 N 247
c. 92 U + 14
7 99 Es + 5 0n
1

24. III. Nuclear Energy
Recall:
Nucleus is composed of proton and neutron
Then, is the mass of an atom equal to the total mass of
all the proton plus the total mass of all the neutron?
Example for a He atom:
Total mass of the subatomic particles
= mass of 2 p+ + mass of 2n0
= 2 ( 1.00728 amu ) + 2 (1.00867 amu)
= 4.03190 amu
And atomic weight of He-4 is 4.00150
Why does the mass differ if the atomic mass = number
of protons + number of neutrons?

25. Mass defect
-mass difference due to the release of energy
-this mass can be calculated using Einstein’s equation
E =mc2
2 11 H + 2 20 H → 42 He + energy
Therefore:
-energy is released upon the formation of a nucleus
from the constituent protons and neutrons
-the nucleus is lower in energy than the component
parts.
-The energy released is a measure of the stability of
the nucleus. Taking the reverse of the equation:
2 He + energy → 2 1 H + 2 0 n
4 1 2

27. Nuclear binding energy per nucleon vs Mass number
nuclear binding energy
nuclear stability
nucleon
23.2

28. -The plot shows the use of nuclear reactions as source of
energy.
-energy is released in a process which goes from a
higher energy state (less stable, low binding energy) to a
low energy state (more stable, high binding energy).
-Using the plot, there are two ways in which energy can
be released in nuclear reactions:
a. Fission – splitting of a heavy nucleus into
smaller nuclei
b. Fusion – combining of two light nuclei to form a
heavier, more stable nucleus.

29. Nuclear binding energy (BE) is the energy required to break
up a nucleus into its component protons and neutrons.
BE + 19F
9 91p + 101n
1 0
E = mc2
BE = 9 x (p mass) + 10 x (n mass) – 19F mass
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
binding energy per nucleon =
number of nucleons
2.37 x 10-11 J
= = 1.25 x 10-12 J
19 nucleons
23.2

30. 23.3

31. Radiocarbon Dating
14
7 N + 0n
1 14
6C + 1H
1
6C
14 14
7
N + -1β + ν
0
t½ = 5730 years
Uranium-238 Dating
92 U
238 206
82Pb + 8 4α + 6 -1β
2
0
t½ = 4.51 x 109 years
23.3

34. Nuclear Fission
235
92 U + 0n
1 90
38Sr + 143Xe + 310 + Energy
54 n
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
23.5

35. Nuclear Fission
Representative fission reaction
235
92 U + 0n
1 90
38Sr + 143Xe + 310 + Energy
54 n
23.5

36. Nuclear Fission
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
23.5

37. Nuclear Fission
Schematic
diagram of a
nuclear fission
reactor
23.5

38. Nuclear Fission
35,000 tons SO2 Annual Waste Production
4.5 x 106 tons CO2
70 ft3
3.5 x 106 vitrified
ft3 ash waste
1,000 MW coal-fired 1,000 MW nuclear
power plant power plant
23.5

40. Nuclear Fusion
Fusion Reaction Energy Released
2
1 H + 1H
2
1H + 1H
3 1
6.3 x 10-13 J
2
1 H + 1H
3 4
2 He + 1n
0
2.8 x 10-12 J
6
Li + 1 H
2
2 4He 3.6 x 10-12 J
3 2
Tokamak
magnetic plasma
confinement
23.6

41. Radioisotopes in Medicine
• 1 out of every 3 hospital patients will undergo a nuclear
medicine procedure
• 24
Na, t½ = 14.8 hr, β emitter, blood-flow tracer
• 131
I, t½ = 14.8 hr, β emitter, thyroid gland activity
• 123
I, t½ = 13.3 hr, γ−ray emitter, brain imaging
• 18
F, t½ = 1.8 hr, β+ emitter, positron emission tomography
• 99m
Tc, t½ = 6 hr, γ−ray emitter, imaging agent
Brain images
with 123I-labeled
compound
23.7

42. Geiger-Müller Counter
23.7

43. 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
γ-ray = 1
β=1
α = 20
23.8

44. Chemistry In Action: Food Irradiation
Dosage Effect
Inhibits sprouting of potatoes, onions, garlics.
Up to 100 kilorad Inactivates trichinae in pork. Kills or prevents insects
from reproducing in grains, fruits, and vegetables.
Delays spoilage of meat poultry and fish. Reduces
100 – 1000 kilorads salmonella. Extends shelf life of some fruit.
Sterilizes meat, poultry and fish. Kills insects and
1000 to 10,000 kilorads microorganisms in spices and seasoning.