1. Reactions that Involve Changes in the Nucleus
Nuclear Chemistry
Reactions that Involve Changes in the Nucleus

2. Stability of a Nucleus Determined by the ratio of neutrons to protons
Up to atomic number 20, stable nuclei have about an equal number of neutrons and protons
For elements above atomic number 20, stable isotopes have slightly more neutrons than protons
There are no stable isotopes for elements above atomic number 82
All radioisotopes listed on Table N are unstable!

3. Transmutation: when the nucleus of an atom changes so that the identity of the element changes (changes in # of protons and in atomic number)
Natural transmutation (ONE REACTANT): when an unstable nucleus (radioisotope) spontaneously decays into a less unstable nucleus
Artificial transmutation (TWO REACTANTS): when one causes a nucleus to change by colliding it with a high-energy particle

4. See the picture on p. 800 of textbook

5. Equations to Represent Nuclear Reactions
The equation MUST obey the laws of conservation of mass and charge
Compare left and right of arrow
Top row for mass: total on the left must equal total on the right
Bottom row for charge: total on the left must equal total on the right

6. Natural Transmutations
Notice the decay mode
Write an equation to represent the decay
The equation MUST obey the laws of conservation of mass and charge
Compare left and right of arrow (total on the left must equal total on the right)

7. Alpha Decay
In alpha decay, a nucleus ejects an alpha particle and becomes a smaller nucleus
** The mass number decreases by 4, and the atomic number decreases by 2.
EXAMPLE FROM TABLE N!!!

8. Beta Decay
In beta decay, a nucleus ejects a beta particle as a neutron becomes a proton
** The mass number remains the same, and the atomic number increases by 1.
EXAMPLE FROM TABLE N!!!

9. Positron Emission
In positron emission, a nucleus ejects a positron particle as a proton is converted to a neutron
** The mass number remains the same, and the atomic number decreases by 1.
EXAMPLE FROM TABLE N!!!

10. Fission and Fusion Reactions: Converting Mass into Energy
The products of both fission and fusion reactions have slightly less mass than the reactants.
Nuclear reaction release more energy than any other reaction with the same mass.
The mass has been converted into energy according to Einstein’s famous equation.
E = mc2

11. Fission
Very large (heavy) nucleus breaks apart into smaller pieces (Starting greater than 200)
The nucleus is hit with a high-energy neutron
Products are very radioactive (waste)
Uncontrolled will produce a chain reaction

12. Fusion
Very small (light) nuclei combining to form a larger nucleus (H and He)
Reaction that occurs on the sun
Products are not radioactive
Requires extremely high temp and pressure

13. Half-Life
The amount of time required for one-half of an original amount of a radioisotope to decay
Look up half-life values on Table N
Values DO NOT depend on temp, pressure, or the original amount (values remain constant)

14. Half-Life Example Problems
Use the “arrow method” where each arrow represents one half-life period
Cut the amount remaining in half for each arrow
If the half-life of a radioisotope is 2.5 hours, what fraction of an original amount remains unchanged after 10 hours?

15. Uses of Radioisotopes: Carbon -14
Carbon-14 is used in “carbon dating”
Carbon-14 is incorporated into living organisms during life processes
One can determine the age of once living material by examining the amount of radiation emanating from the sample
The amount of radiation decreases as the carbon-14 decays

16. Uses of Radioisotopes: Uranium-238/Lead-206 Ratio
Unstable Uranium-238 decays through a series of steps to become the more stable Lead-206 isotope
As the amount of U-238 decreases, the amount of Pb-206 increases
Scientists can date rocks and other geological formations by determining and examining the ratio of U-238/Pb-206

17. Uses of Radioisotopes: Phosphorus-31 and C-14 Tracers
A tracer is a radioisotope used to follow the path of a material in a substance
Doctors and radiologists can inject patients with P-31 and detect when the radioisotope travels in the body
P-31 in fertilizer can help scientists determine the proper amounts and timing of fertilizing plants and crops
Scientists can use C-14 to map the path of carbon compounds in metabolic processes

18. Uses of Radioisotopes: Medical Applications of I-131
Ideal radioisotopes used in medicine have short half-lives and are eliminated from the body quickly
Iodine-131 is used for both the detection and treatment of thyroid disorders
I-131 accumulates in the thyroid gland
Large doses of I-131 can destroy thyroid tissue to benefit patients with hyperthyroidism

19. Uses of Radioisotopes: Medical Applications of Co-60
Ideal radioisotopes used in medicine have short half-lives and are eliminated from the body quickly
Cobalt-60 is useful in radiation treatments to destroy cancerous cells
Co-60 emits large amounts of gamma radiation as it decays
When aimed at cancerous tumors, the gamma radiation can kill rapidly growing cancer cells

20. Uses of Radioisotopes: Medical Applications of Tc-99
Ideal radioisotopes used in medicine have short half-lives and are eliminated from the body quickly
Technetium-99 is used to help diagnose or detect cancerous tumors
Cancerous cells rapidly absorb Tc-99
Tc-99 accumulates in cancerous tumors so that the tumors are easily detected with a scan

21. Uses of Radioisotopes: Food Industry using Co-60 and Cs-137
Both cobalt-60 and cesium-137 are good sources of gamma radiation
Intense gamma radiation can kill bacteria in spices, produce and meat
As the gamma radiation kills bacteria, foods will not spoil as quickly and consumers will not suffer from bacterial infections