1. Unit 12- Nuclear Chemistry
Nucleon
Positron
Radioactive
Radioisotope
Tracer
Transmutation
Alpha particle
Artificial transmutation
Beta particle
Fission
Fusion
Gamma ray
Half-life
Natural transmutation

2. Nuclear Reactions Involve the nucleus of an atom
nucleons- protons and neutrons
The nucleus opens, and protons and neutrons are rearranged
This releases a tremendous amount of energy that holds the nucleus together – called binding energy
Transmutation- when an atomic nucleus changes into the nucleus of another element
“Normal” Chemical Reactions involve electrons, not protons and neutrons
Strong force- what holds the nucleus together acts on particles that are close together

3. Nuclear stability Ratio of neutrons to protons
Belt is located above a 1:1 ratio of neutrons to protons but below a 2:1 ratio

4. Nuclei with atomic numbers above 83 are unstable
Therefore they are radioactive
Too many neutrons, high neutron:proton ratio
What is a radioactive atom?
An unstable nucleus that spontaneously decays to form a more stable product
Called a radioisotope

5. When a nucleus decays it will emit radiation in these possible forms:
Alpha particle- α
Helium nucleus
Beta particle-β
Has a 1- charge
Positron- has a 1+ charge
Similar to beta particle but opposite charge
Gamma rays-γ
Almost all nuclear decay emits some; similar to X-rays but has greater E~ high energy photons
Table O!!

6. Penetrating ability of radiation
Gamma

7. Deflection of Particles
Negative  
Positive

8. Alpha Emission (decay)
226 4
222 Ra He + Rn 88 2 86
Alpha Particle
Radium-226
Radon-222
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Mass Number (P+N)
226 = 4 +
222 =
Atomic Number (protons only) 88 2 + 86
Nuclide= a particular type of nucleus, characterized by a specific atomic number and nucleon number
Nucleons (protons and neutrons) are rearranged but conserved
The Law of Conservation of Matter is obeyed
Atomic # decreases by 2, atomic mass decreases by 4
Table N

9. Alpha Emission Example:

10. Beta Emission (decay) U e + Np
239
239 U e + Np 92 -1 93
Beta Particle
Uranium-239
Neptunium-239
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Mass Number (P+N)
239 = +
239 =
Atomic Number (protons only) 92 -1 + 93
Law of Conservation is followed
Atomic number goes up by one
Atomic mass remains unchanged

11. Beta Emission Example:

12. Positron Emission (decay)
207
207 Po e + Bi 84 +1 83
Positron
Bismuth-207
Polonium-207
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Mass Number (P+N)
207 = +
207 = +
Atomic Number (protons only) 84 +1 83
Law of Conservation is followed
Atomic number goes down by one
Atomic mass remains unchanged

13. Positron Emission Example:
Same result when a nucleus captures its least energetic electron
K-capture

14. Gamma Emission
The nucleus has energy levels just like electrons, but they involve a lot more energy.
When the nucleus becomes more stable, a gamma ray may be released.
This is a photon of high-energy light, and has no mass or charge.
The atomic mass and number do not change with gamma.
Gamma may occur by itself, or in conjunction with any other decay type

15. Gamma Emission Example:

16. Rules for Writing Nuclear Equations
The mass on each side of the equation must be equal
The charges on each side of the equation must be equal
General Format
X X+ Y A Z a z
A-a
Z-z

20. Types of transmutations
Natural-
The decay methods already discussed
Alpha, beta, positron, gamma
Natural; due to unstable nuclei
Has 1 reactant
Artificial- (2 types)
1- collide charged particle with target nucleus
Accelerate protons or alpha particles to overcome repulsive forces from nucleus
1- the particles have to have enough E to overcome the repulsive forces between positively charged particle and positively charged nucleus
this E is supplied by accelerating particles by magnetic or electrostatic fields, these machines are called synchotrons
Most of the elements from 93 on up (the “transuranium” elements) were created using particle accelerators.

21. 2- collide neutron with target nucleus
Neutrons are obtained as nuclear reaction by-products; they are captured by nucleus’s strong force
Used to prepare radioisotopes from stable nuclei
Has 2 reactants
2- the reactions that donate the neutrons are similar to the reactions that create electricity. Neutron has no charge so it isn’t repelled from the nucleus, it’s captured by the forces that hold the protons and neutrons in nucleus
Cyclotron linear accelerator

22. Nuclear Fission
A heavy nucleus is split into two smaller nuclei with release of energy
Mass is converted to energy (E = mc2) 1
235 92
141 n  1 + U Kr + Ba + 3 n 92 36 56
Fission- 2 s’s so it splits 1 into 2
Fusion – 1 s makes 1 fuses

23. Because neutrons are reactants and products, a chain reaction occurs
Fission
Neutron causes a large nucleus to split into smaller ones.
Used in nuclear reactors.
10n +
23592U  +
9136Kr +
3(10n)
14256Ba
Because neutrons are reactants and products, a chain reaction occurs

24. Nuclear Fission

27. Nuclear Fusion Two lighter nuclei are fused to form a heavier nucleus1 4  H He + 2 4 e
+ energy (E = mc2) 1 2 -1 2  4 2 H He
+ energy (E = mc2) 1 2
20% of our electricity for our country is nuclear
Waste is stored in spent fuel pools
advantage: products aren’t highly radioactive like fission
The process that occurs in stars and thermonuclear weapons (hydrogen bombs)

28. Fusion
Combining of light nuclei to form heavier ones.
Lots of energy required to start it, but lots of energy released.
In Sun:
The equations on this slide happen on the sun are still unable to do on Earth due to the tremendous temperature and pressure needed tor the reaction to take place
4(11H) 
2(0+1e)
42He +

30. Energy in Nuclear Reactions
Nuclear reactions result in a loss of a small amount of mass and, therefore, release a large amount of energy.
E = mc2
Over 1 billion times more energy is produced in a nuclear reaction than in any other type of reaction
The matter that’s converted into the energy is called the MASS DEFECT

31. Radioactive decay
substances decay at a constant rate, regardless of temperature, pressure, etc
Random event that can’t be predicted
Table N shows mode of decay for some radioactive elements
More to Table N than this! 

32. Half-life
The time it takes for half the atoms in a given sample of an element to decay
Each radioisotope has its own half-life
Shorter half-life = more unstable

33. Half-life equations Table T in reference tables n= t/T
n = number of half-lives
t= time elapsed
T= half-life
Fraction of remaining: (1/2)n or (1/2)t/T
Original mass= final mass x 2n

34. Decay of 20. 0 mg of Oxygen-15. What remains after 3 half-lives
Decay of 20.0 mg of Oxygen-15. What remains after 3 half-lives? After 5 half-lives?
Has a half life of 122 seconds
20 mg
10 mg
5 mg
2.5 mg

35. Going Forwards in Time
How many grams of a 10.0 gram sample of I-131 (half-life of 8 days) will remain in 24 days?
#HL = t/T = 24/8 = 3
Cut 10.0g in half 3 times: 5.00, 2.50, 1.25g

36. Going Backwards in Time
How many grams of a 10.0 gram sample of I-131 (half-life of 8 days) would there have been 24 days ago?
#HL = t/T = 24/8 = 3
Double 10.0g 3 times: 20.0, 40.0, 80.0 g

37. Radioactive Dating
A sample of an ancient scroll contains 50% of the original steady-state concentration of C-14. How old is the scroll?
50% = 1 HL
1 HL X 5730 y/HL = 5730y

38. Uses of Radioisotopes Radioactive dating
Carbon-14 for dating organic remains
Potassium-40 for dating rocks
Uranium-238 for determining the age of the earth

39. Radiation therapy for cancer
Destroy cancer cells (can damage healthy cells)
Irradiation of food
Cobalt-60 produces gamma rays- kill bacteria
Tracers
Carbon-14 for photosynthesis
Iodine-131 for thyroid disorders
Technetium-99 for diagnosis of brain tumors
Carbon-13 for real-time brain imaging (PET Scan)
Why do these uses require short half-lives?
Short half-lives so they don’t stay in body long

40. Other Uses of Radioactive Isotopes
C-14: Carbon Dating (Finding Age of Organic Material)
U-238: Geological Dating (Finding Age of Inorganic Material)
U-235: Nuclear Power Plant Fuel
P-31: Tracer in Plant Fertilizer
I-131: Detection and Treatment of Thyroid Conditions
Tc-99: Cancer Detection and Location
Co-60: Cancer Treatment and destruction of bacteria
Cs-137: Destruction of Bacteria