1. Nuclear Chemistry

2. Aim #1: What is Nuclear Chemistry?
A naturally radioactive element will emit energy without the absorption of energy from an outside source.
The nucleus of an element becomes radioactive because of an unstable ratio of protons to neutrons in the nucleus.
All elements with atomic number greater than 83 (Bi) are unstable and will spontaneously decay.

3. Stability
The ratio of neutrons to protons in stable nuclei is approximately 1:1
Belt of stability
Atoms with atomic numbers above 82 have no stable isotopes

4. Belt of Stability

5. Radioactivity Discovered by Marie Curie
Unstable nuclei break apart or decay
Decaying nuclei release/emit particles and energy
Alpha particle
Beta particle
Positron
Gamma ray

6. Common Radioactive Emissions
(Table O)
Particle
Mass
Charge
Symbol
Penetrating Power
Alpha
(helium)
4 amu
2 +
Low
Beta
(electron)
~0 amu 1-
Moderate
Positron 1+
Gamma
(energy)
High

7. Penetrating Ability

8. Aim#2: How do we write transmutation reactions?
When the nucleus of one element is changed into the nucleus of a different element
2 types:
Natural transmutation (1 reactant)
Artificial transmutation (at least 2 reactants)

9. Natural Transmutation
Alpha decay
An alpha particle is emitted

10. Natural Transmutation
Beta Decay
a beta particle is emitted

11. Natural Transmutation
Positron Emission
Conversion of a proton to a neutron

13. Write a nuclear equation showing what forms when
Sample Problem
Write a nuclear equation showing what forms when
radon-222 decays
Step 1: Determine the type of emission by looking on Table N
Step 2: Look up the atomic number of the known element and write an equation showing the known information
Step 3: Subtract the weight and charge of the emission from the weight and charge of the original element to determine the weight and charge of the new element
Step 4: Identify the new element based on the nuclear charge or atomic number

14. Aim# 3: What is Nuclear Energy
Produced by a nuclear reaction that converts mass into energy. Produces on the order of a billion times more energy than a chemical reaction

15. Artificial Transmutation
Human made reactions in which a nucleus is bombarded with a high speed particle which causes the nucleus to emit a proton or neutron
May use particle accelerators to give charged particles enough KE to overcome the repulsion that exist between two nuclei
At least two reactants
Examples:
Importance: this is how human made elements are produced

16. Fission Reactions
The splitting of a heavy nucleus into two or more lighter nuclei.
Nucleus must have a high atomic number, process requires a neutron to collide with the heavy nucleus
Nuclear reactors, atomic bomb

17. Fission
A chain reaction can occur where the neutrons released by fission of one nucleus trigger fission in another nuclei
Importance- an uncontrolled chain reaction results in a nuclear explosion (atomic bomb), a controlled chain reaction can be used as a source of energy (nuclear reactor)

18. Fission Benefits Problems The fuel lasts longer than fossil fuels
CO2 and smoke products are not produced, therefore not contributing to air pollution
Releases large amounts of energy
Problems
Fuels and products are radioactive
Possibility of a nuclear accident

20. Fusion Two light nuclei combine to form heavier nuclei
Occurs in the sun
Produces a huge amount of energy
Hydrogen bomb

21. Fusion, fuels The fuels for this reaction are hydrogen isotopes
(Hydrogen- 1,2 or 3)
H-1 reacts the slowest
H-2 is obtained from heavy water and H-3 can be produced in a nuclear reaction

22. Fusion Benefits Use inexpensive, plentiful fuel
Produce almost no harmful radioactive wastes
Problems
Extremely high activation energy to trigger the reaction
Extremely high temperatures, difficult to control

24. Mass Defect
For both fission and fusion reactions, the total mass of the products is less than the total mass of the reactants
Mass defect- when matter has been converted into energy

25. The mass of a proton is 1.00728 amu
The mass of a neutron is amu
Carbon-12 has a mass of exactly 12 amu
If you add up 6 protons and 6 neutrons, you get more than 12 amu
The mass of 6 protons and 6 neutrons is amu
The mass of a carbon nucleus is less than the sum of its parts!!!

26. Uses of Radioisotopes Radioisotope Use Carbon-14 (C-14)
Dating previously living materials, tracer
Uranium-238 (U-238)
Pb- 206
Dating rocks, geological formations
Phosphorous-31 (P-31)
Used in fertilizer to trace the intake of phosphorous by plants
Iodine-131 (I-131)
Detection and treatment of thyroid conditions

27. Radioisotope
Use
Cobalt (Co-60)
Can be used for treating cancer
Radium
Technetium-99 (Tc-99)
Location of tumors

28. Radiation Risks
Difficult to store and dispose of nuclear waste products because of their long half lives

29. How do we solve Half Life problems?
Radioactive isotope disintegrate at characteristic rates.
The amount of time it takes for half of a radioactive sample to decay
Table N!!

30. Sample Problem
If I initially have 100g of a sample and its half life is 5 seconds, how long will it take for the sample to contain only g?
How many half lives did the sample undergo?
What fraction of the original sample remains?

31. Typical Half Life Graph