1. Nuclear Chemistry
Chapter 28

2. Nuclear Reactions Reactions that occur in the NUCLEUS.
Cannot be slowed down, speeded up, or turned off.

3. Chemical Reactions vs. Nuclear Reactions
Chemical Rxns:
Atoms gain stability by attaining stable electron configurations
Nuclear Rxns:
Unstable isotopes (radioisotopes) gain stability by making changes within their nuclei
Not affected by pressure, temp., or catalysts

4. Radioactivity
Radioisotopes are radioactive because they have unstable nuclei.
Stability of the nucleus:
Ratio of neutrons to protons
Too many or few neutrons relative to the # of protons = unstable nucleus

5. Radioactive Decay
The process in which an unstable nucleus loses energy by emitting radiation.
Spontaneous process and doesn’t need any input of energy.
Unstable radioisotopes are eventually transformed into stable (nonradioactive) isotopes of a different element.

6. 3 Types of Radiation
ALPHA () radiation—could be stopped by a sheet of paper
+2 charge --helium atom 42He
BETA () radiation—could be stopped by a sheet of aluminum
-1 charge --high-speed electron

7. Types of Radiation (cont.)
GAMMA () radiation—could be stopped by lead
No charge --no mass

8. Ernest Rutherford
He used uranium and thorium, and put them in a magnetic field
Alpha and beta particles are deflected by a magnetic field.
Gamma rays moved through the field without being affected.

9. Nuclear Stability Stable nuclei do not decay or change with time
Stability depends on its neutron-to-proton ratio
Out of the 1500 known nuclei, 264 of them are stable

11. Half-Life
Half-life (t1/2): the time required for one-half of the atoms of a radioisotope to emit radiation and to decay to products

12. Example: Half-life
Assume there are 2.00 g of N-13. How many grams of N-13 will exist after 3 half-lives?
# of half-lives Mass of N-13 g g g g

13. Uses For Radioisotopes
C-14
Used to date fossils and artifacts
Many artificially produced radioisotopes have very short half-lives
Great advantage in nuclear medicine (Co, I)
U-238 (half-life of 4.5 x 109 years)
Used to date rocks as old as our solar system

14. Transmutation Reactions
Transmutation: the conversion of an atom of one element to an atom of another element
Some transmutations occur naturally through radioactive decay (, )
All other transmutations are artificially done in laboratories
High-energy particles bombard the nucleus of an atom

15. Transuranium Elements
Elements in the periodic table with atomic numbers above 92
None occur in nature and all are radioactive
Synthesized in nuclear reactors and nuclear accelerators

16. Nuclear Fission and Fusion
Fusion: Two nuclei combine to produce a nucleus of heavier mass.
Fission: Splitting of a nucleus into smaller fragments.
Nuclei of certain isotopes are bombarded with neutrons 9

17. Fission

18. Fission Produces a Chain Reaction

19. Nuclear Fission Enormous amounts of energy released
1 kg of U-235 releases an amount of energy equal to that generated in an explosion of 20,000 tons of dynamite
Atomic bombs are devices that start uncontrolled nuclear chain reactions

20. Nuclear Fission (cont.)
Fission can be controlled so that energy is released more slowly
Nuclear reactors—heat removed from the reactant core by a coolant fluid (water)
Control rods used to control neutron absorption

21. Nuclear Fusion Thermonuclear rxn
Energy released from the sun
Fusion rxns release more energy than fission rxns
Takes place only at very high temperatures—in excess of 40,000,000C
Fusion products usually not radioactive

22. Nuclear Fusion (cont.) Hydrogen Bomb Matter exists as a plasma
High temps required to initiate fusion rxns
Atomic bomb—used as a triggering device to set off the H-bomb
Matter exists as a plasma