1. Nuclear Chemistry

2. Nuclear Reactions vs. “Normal” Chemical Changes
“Normal” Chemical changes involve electrons, not protons and neutrons
Nuclear Reactions involve the NUCLEUS
Protons and neutrons (or their parts)are rearranged or released from the nucleus
Energy is released

3. Nuclear Reactions
Elements that undergo nuclear reactions are said to be radioactive
Not all elements are radioactive
Elements with atomic numbers greater than 83 have no stable isotopes – they are all radioactive
Some elements with atomic numbers less than 83 have radioactive isotopes
Radioactivity
The disintegration or decay of an element’s nucleus into smaller pieces
This decay results in the emission of particles and/or radiant energy

4. Nuclear Reactions Remember isotopes…
Atoms of the same element that have different numbers of neutrons
Most isotopes are stable – those that are radioactive have an unstable ratio of protons and neutrons in their nucleus
Emitting a particle from their nucleus creates a more stable ratio
It also changes the nucleus into a different element!

5. Nuclear Reactions
Reactions involving the decay of the nucleus and changing into a new element are called transmutation reactions
Two kinds of transmutation reactions:
Natural transmutation
Elements that naturally emit energy without the absorption of energy from an outside source
Artificial transmutation
Causing an otherwise stable nucleus to become radioactive
Nuclear fission and nuclear fusion

6. Natural Transmutation
There are several types of radiation that an unstable nuclei can emit to attain a more stable atomic configuration
Table O – Symbols used in Nuclear Chemistry – shows the radiation that can be emitted
Note - gamma radiation is not a particle. It is only energy.

7. Natural Transmutation
The three decay modes are:
Alpha decay
The release of an alpha particle from the nucleus
Beta decay
The release of a beta particle from the nucleus
Positron decay
The release of a positron particle from the nucleus

8. Natural Transmutation
Table N – Selected Radioisotopes
Shows the decay mode that a particular radioisotope goes through

9. Natural Transmutation
Just as a balanced chemical reaction must always be written for a “normal” chemical reaction a balanced nuclear reaction can be written as well.
These are examples of balanced nuclear equations
One element becomes another
The particles involved are balanced
The sum of the mass numbers and the sum of the atomic numbers on each side are equal

10. Natural Transmutation
Steps for writing and balancing a nuclear reaction
Write and balance the nuclear reaction for radium-226.
Step 1: Write the notation for the radioactive isotope as the reactant
Step 2: Look on Table N for the decay mode of the radioisotope
radium – 226 = α
Step 3: Look on Table O for the symbol of the decay mode. This is one of the products, write the symbol of the particle as a product
Step 4: The second product is determined by first balancing the mass number and atomic number and then looking on the periodic table to determine what element has that atomic number
226
222 4 Rn Ra He + 2 86 88

11. Natural Transmutation
The nucleus of radium – 226 emits an alpha particle and the decay product is radon - 222

12. Natural Transmutation
Write the balanced nuclear equation for the decay of iodine - 131
131
131 I β Xe + 53 -1 54

13. Natural Transmutation
Neon – 19 decays by positron emission. Write the balanced nuclear equation. 19 Ne β 19 F + 10 +1 9

14. How Fast is Radioactive Decay?
Half – Life
The time for half of a sample of a radioisotope to disintegrate
Example: The half life of iodine – 131 is 8 days. If we started with a 100 g sample of I – 131, after 8 days only 50 g of I-131 would remain. After another 8 days only 25 g of I-131 would remain.
Table N – Selected Radioisotopes
Shows the half – life of the selected radioisotopes
In the above example – after the first 8 days 50 g of I-131 remain. What are the other 50 grams of the sample?

15. Half - Life
Although formulas have been derived for calculating the mass of a radioactive isotope remaining after a given time, it is more convenient to set up a T-chart of mass and time
2 things to remember
Find half-life in reference table N
Begin your table with time zero and the original mass of the sample

16. Half - Life Time Mass 0 days 2.00 mg 44.5 days 1.00 mg 89 days
An example
Iron - 59 is used in medicine to diagnose blood circulation disorders
The half life of iron – 59 is 44.5 days
How much of a 2.00 mg sample will remain after days?
After days there will be mg of the 2.00 mg sample of Iron – 59 left

17. Artificial Transmutation
Radioactive elements can also be produced by bombarding the nuclei of stable atoms with high energy particles such as protons, neutrons and alpha particles (sort of like shooting a bullet at the nucleus).
This type of radioactivity is called artificial transmutation and can be identified by reactants
Natural transmutation can be identified by 1 reactant

18. Artificial Transmutations
Particle Accelerators
When the nuclei of stable atoms are bombarded by accelerated particles, the nuclei become unstable and may cause the formation of isotopes of new elements
Particle accelerators of various types are used to give charged particles enough kinetic energy to overcome electrostatic forces
Once this occurs they can penetrate nuclei of target atoms and artificial transmutation will occur
Acceleration is accomplished by means of manipulation of electric and magnetic fields

19. Artificial Transmutation
What radioactive isotope is produced in the following bombardment of boron?
10B He n 13 N 5 2 7

20. Nuclear Energy
Nuclear reactions involve energies that are millions of times greater than those found in “normal” chemical reactions
Energies of these magnitudes are often the result of the conversion of mass into energy

21. Nuclear Fission Nuclear fission
Splitting of a heavy nucleus into two lighter nuclei
Only elements of high atomic number can be go through nuclear fission
When heavy elements undergo fission, the new elements formed are more stable than the parent element
Type of reaction carried out in nuclear reactors

22. Nuclear Fission
Bombardment of the radioactive nuclide with a neutron starts the process.
Neutrons released in the transmutation strike other nuclei, causing their decay and the production of more neutrons which can strike other nuclei .
This process continues in what we call a nuclear chain reaction
It also results in the liberation of energy
The energy liberated results from the conversion of mass into energy

23. Nuclear Fission
AND ENERGY!
Uranium – 235 is the most common reactant of a nuclear fission reaction

24. Nuclear Fission In nuclear reactors the chain reaction is controlled
In an atomic bomb the reactions are not controlled
If there are not enough radioactive nuclides in the path of the ejected neutrons, the chain reaction will die out

25. Nuclear Fission Problem Radioactive Wastes
Both the fuels and products of fission reactions are radioactive which poses a health problem if people are exposed
Possibility of nuclear accident
Or theft of fuels from reactor sites
To produce nuclear weapons
Radioactive Wastes
Solid and liquid waste are sealed in containers that are stored under ground or in isolated areas
Gaseous radioactive wastes are stored until they decay to safe levels and then dispersed into the atmosphere
The wastes of nuclear fission often have long half lives which causes them to be radioactive for long periods of time

26. Nuclear Fusion
Combining of two light nuclei to form one nucleus of larger mass
Energy released is much greater than that in fission reactions
Fusion reactions – require temperatures of 40,000,000 K to sustain the reaction
The mass of the new nucleus is less than the sum of the masses of the light nuclei
The difference in mass represents the mass that was converted to energy in the process
Occurs naturally in the sun and stars

27. Nuclear Fusion Fusion would be a superior method of generating power
The good news:
The products of the reaction are not radioactive
The bad news:
In order to achieve fusion, the material must be in the plasma state at several million Kelvin

28. Fusion Nuclear Fusion 2H + 3H 4He + 1n + Small nuclei combine Energy 21 1

29. Fission vs. Fusion F I S O n F u S I O n Danger of meltdown
U is limited
Danger of meltdown
Toxic waste
Thermal pollution
Fuel is abundant
No danger of meltdown
No toxic waste
Not yet sustainable

30. Uses of Radioisotopes Based on Chemical Reactivity
Can be used to trace the course of a reaction
Usually used in nuclear medicine
Based on Radioactivity
Isotopes with very short half-lives are used for diagnostic purposes
Tumors can be located – Te-99 used to locate brain tumors, I-131 used to locate thyroid disturbances
Based on Half-life
Used to determine the age of fossils and rocks
Radiochemical dating
Radiation Treatment
Large doses are used to kill cancerous cells in target organs
Food Preservation
Isotopes can be used to destroy bacteria, mold and eggs of insects

31. Nuclear Weapons Atomic Bomb Hydrogen Bomb
Chemical explosion is used to form a critical mass of 235U or 239Pu
Fission develops into an uncontrolled chain reaction
Hydrogen Bomb
Chemical explosion  fission  fusion
Fusion increases the fission rate
More powerful than the atomic bomb