1. Structure and Stability of Nuclei, Fission, Fusion, and Radiation
Nuclear Chemistry
Structure and Stability of Nuclei, Fission, Fusion,
and
Radiation

2. Standards
11. Nuclear processes are those in which an atomic nucleus changes, including radioactive decay of naturally occurring and human-made isotopes, nuclear fission, and nuclear fusion. As a basis for understanding this concept: a. Students know protons and neutrons in the nucleus are held together by nuclear forces that overcome the electromagnetic repulsion between the protons. 11. b. Students know the energy release per gram of material is much larger in nuclear fusion or fission reactions than in chemical reactions. The change in mass (calculated by E = mc2 ) is small but significant in nuclear reactions. 11. c. Students know some naturally occurring isotopes of elements are radioactive, as are isotopes formed in nuclear reactions. 11. d. Students know the three most common forms of radioactive decay (alpha, beta, and gamma) and know how the nucleus changes in each type of decay. 11. e. Students know alpha, beta, and gamma radiation produce different amounts and kinds of damage in matter and have different penetrations. 11. f.* Students know how to calculate the amount of a radioactive substance remaining after an integral number of half-lives have passed. 11. g.* Students know protons and neutrons have substructures and consist of particles called quarks.

5. Nuclear Chemistry has to do with an atom’s nucleus plural of
nucleus = nuclei
What’s a nucleus?
Let’s review
An atom’s nucleus contains
almost all of an atom’s mass,
but takes up very little of it’s volume.

6. Subatomic Particles the particles that make up an atom
Protons – high mass, positive charge. Found in nucleus.
Neutrons – high mass, no charge. Found in nucleus.
Electrons – low mass, negative charge. Found orbiting around nucleus. (abbreviated e– )

7. Comparison of Masses
Electron
Proton
Neutron

8. An Atom
Size of atom
Size of nucleus
2 protons = He = helium

9. Basic Electrical Charge Laws
+ and – : Attract
(pull together)
– and – : Repel
(push away)
+ and + : Repel
Like charges repel and Opposites attract

10. So why don’t the protons in the nucleus fly apart?
nuclear
force
is stronger over short distances
electrostatic
force
is stronger over long distances

11. Key Na 11 Atomic Number Number of Protons
Sodium
22.99
Atomic Number
Number of Protons
Number of Electrons (when atom is neutrally charged)
Property unique to each element

12. Key Na 11 Average atomic mass* Sodium 22.99
Weighted Average number of Protons and Neutrons (approximately)

13. Isotopes
When atoms have the same number of protons, but different numbers of neutrons, they are called isotopes.
Examples:
Carbon-14 has 6 protons and 8 neutrons.
Carbon-12 has 6 protons and 6 neutrons.
Carbon-14 is found more often in living organisms than in non-living matter. It also undergoes radioactive decay – which is why it is used for fossil dating.

14. Isotopes More Examples: Uranium-238 has 92 protons and 146 neutrons.
Uranium-235 is more rare in nature than Uranium-238, but it also undergoes nuclear chain reactions more easily, which is why small amounts of Uranium-235 are used in nuclear weapons and nuclear power plants.
Some isotopes are more stable than others.

15. Which isotope is more abundant?
Neon-20
Neon-22
How many neutrons in each?
Neon-20
Neon-22
20 – 10 = 10 neutrons
22 – 10 = 12 neutrons

16. Which isotope is more abundant?
Bromine-79
Bromine-80
How many neutrons in each?
Bromine-79
Bromine-80

17. Lead has two isotopes with the following relative amounts:
What would the average atomic mass calculate to be?
0.8(207) + 0.2(208) =
207.2

18. Chlorine has two stable isotopes:
??% x
100 –??%
1 – x
What are the relative abundances (in %) of each isotope?
-2x = -1.55
x(35) + (1-x)(37) = 35.45
35x – 37x + 37 = 35.45
x = 0.775
-2x + 37 = 35.45
–37 –37
-2x = -1.55

19. Chlorine has two stable isotopes:
77.5%
0.775
22.5%
0.225
What are the relative abundances (in %) of each isotope?
-2x = -1.55
x(35) + (1-x)(37) = 35.45
35x – 37x + 37 = 35.45
x = 0.775
-2x + 37 = 35.45
–37 –37
-2x = -1.55

21. So why don’t the protons in the nucleus fly apart?
nuclear
force
is stronger over short distances
electrostatic
force
is stronger over long distances

22. Sometimes these forces are overcome.
Fission – a nucleus breaks apart.
(ex. atomic bomb, nuclear power plants,
radioactive decay)
Fusion – a nucleus merges with another.
(ex. the sun, hydrogen bomb,
experimental fusion reactors)

24. γ He e Both fission and fusion release radiation.
It is called radiation because it radiates out.
Symbol
Common Types of Radiation He 4 2
α (alpha): helium nucleus at high speed.
β (beta): electron at high speed.
γ (gamma): high energy photon. e -1
harder to block γ

25. β+ n p Symbol Other Types of Radiation neutron at high speed.1
neutron at high speed.
Proton (or hydrogen nucleus) at high speed.
β+ positron at high speed (the anti-matter version of an electron). p 1 β+ 1

26. atomic mass Na 23 11 Na 22 11
number
of protons

27. We can use conservation of mass and charge to figure out nuclear reactions just like chemical reactions. U
238 92 He 4 2 +
??? Th
234 90 e -1 +
???

28. We can use conservation of mass and charge to figure out nuclear reactions just like chemical reactions. U
238 92 He 4 2 + Th
234 90 Th
234 90 e -1 +
???

29. We can use conservation of mass and charge to figure out nuclear reactions just like chemical reactions. U
238 92 He 4 2 + Th
234 90 Th
234 90 e -1 + Pa
234 91

31. Half-Life
Half-life – how much time has passed when half of the original amount remains.
How much of the original remains after two half-lives?
How much after three half-lives?
How much after four half-lives?
or 50 % 1 2
or 25 % 1 4
or % 1 8
or % 1 16

32. Table of Half-Lives Isotope Name Symbol Half-Life Uranium-238 23892U
4.51 × 109 years
Uranium-235
23592U
7.1 × 108 years
Carbon-14
146C
5,730 years
Strontium-90
9038Sr
28 years
Cobalt-60
6027Co
5.27 years

33. Table of Half-Lives Isotope Name Symbol Half-Life Thorium-234 23490Th
24.1 days
Protactinium-234
23491Pa
6.75 hours
Polonium-218
21884Po
3.08 minutes
Radon-219
21986Rn
4.00 seconds
Polonium-214
21484Po
1.6 × 10-4 seconds

34. As a archaeologist you find a dead rat that contains 0
As a archaeologist you find a dead rat that contains grams of Carbon-14. A rat that died a year ago has 0.01 grams of Carbon-14. How long ago did the rat die?
t½ = 5,730 years g
0.01 g 1
11.1 = 1 2 1 4 1 8 1 16 1 32 1 64
1 H.L.
2 H.L.
3 H.L.
4 H.L.
5 H.L.
6 H.L.

35. As a archaeologist you find a dead rat that contains 0
As a archaeologist you find a dead rat that contains grams of Carbon-14. A rat that died a year ago has 0.01 grams of Carbon-14. How long ago did the rat die?
t½ = 5,730 years
3(5,730) =
17,190 years 1
11.1
4(5,730) =
22,920 years 1 8 1 16
17,190 – 22,920 years ago
3 H.L.
4 H.L.

36. 2013 – 1963 = 50 years 50 yr 28 yr = 1.8 half-lives 1 2 1 4 1 8 1 16 1
Strontium-90 is one of the “fallout” products from atmospheric testing of nuclear weapons. If there were 50,000 grams of Strontium-90 in the U.S. southwest region when the 1963 testing ban began, how much Strontium-90 currently remains? t½ = 28 years
2013 – 1963 =
50 years
50 yr
28 yr =
1.8 half-lives 1 2 1 4 1 8 1 16 1 32 1 64
1 H.L.
2 H.L.
3 H.L.
4 H.L.
5 H.L.
6 H.L.

37. Radioactive Decay Formulas
A = A0 e
-( )t
ln (2) t½ 1
A0 = original amount
A = current amount
t = current time
t½ = half-life
t½ = A0 A
ln (2)
ln ( ) t 2
t = A0 A
ln ( )
ln (2) t½ 3

38. Energy-Mass Equivalence
Sometimes in nuclear change a small amount of the mass disappears. It has been converted to a large amount of energy according to the formula:
E = mc2
energy = (mass) × (speed of light)2
J = kg × (m/s)2
speed of light: c = 3 × 108 m/s

40. Fission Nuclear Reaction

41. 4 e– in valence shell

45. Which isotope is more abundant?
Lead-207
Lead-208
How many neutrons in each?
Lead-207
Lead-208