1. Chapter 22
Nuclear Chemistry

2. Radioactive decay
– An unstable isotope that undergoes spontaneous disintegration of a nucleus into a lighter nucleus (more stable)
Radioisotopes
Nuclei that undergo radioactive decay
May produce one or more types of radiation

3. Natural Radioactivity
Background radiation
What occurs from natural sources
>80% of radioactivity exposure

4. Types of Radiation
Ionizing radiation – knocks electrons out of atoms or groups of atoms
Produces charged species – ions
Charged species that cause damage

5. Differences Between Chemical and Nuclear Reactions

6. Nuclear Equations Elements may change in nuclear reactions
Total mass and sum of atomic numbers before and after must be the same
MUST specify isotope

7. Alpha Decay Nucleus loses  particle
Alpha particle will be on the right side of the arrow
Mass decreases by 4 and atomic number decreases by 2

8. Beta Decay Nucleus loses  particle
Beta particle will be on the right side of the arrow
No change in mass but atomic number increases by one

9. Electron Capture
Nucleus absorbs an electron and then releases an X-ray
Electron will be on the left side of the arrow
Mass number stays the same and atomic number decreases by one

10. Positron Emission Loses a positron
Equal mass but opposite charge of an electron
Decrease in atomic number by 1 and no change in mass +

11. Gamma Radiation Release of high-energy photon
Typically occurs after another radioactive decay
No change in mass number or atomic number

12. Nuclear Chemistry
Nuclear reaction – a reaction that affects the nucleus of an atom Nuclear radiation – particles or electromagnetic radiation emitted from the nucleus during radioactive decay

13. Nuclear Chemistry Nuclear equation parent nuclide daughter nuclide
Parent nuclide – the heaviest nuclide in a decay series
Daughter nuclide – the nuclide produced by the decay of the parent nuclide

14. 5/20/09 Bellwork (pg. 68)
Complete the following nuclear equations & name the particle that goes in the blank. 14 C  14 N + _____ 6 7 _______  4 He Th Mg  0 e- + _______ 12 -1

15. Nuclear Medicine Used for two purposes
Therapeutic – treat or cure disease using radiation
Diagnostic – obtain information about patient’s health

16. Uses of Radioisotopes Tracers
Radioactive atoms that are incorporated into substances so that the movement of the substance can be followed
Many different isotopes used
Can measure specific things
Iodine-131 to locate tumors in thyroid
Selenium-75 to look at pancreas
Gadolinium-153 to determine bone mineralization

17. Penetrating Power of Radiation
The more mass the particle has, the less penetrating it is
The faster the particle is, the more penetrating it is

18. Prevent Radiation Damage
To minimize damage
Stay a distance from radioactive sources
Use shielding; need more with more penetrating forms of radiation

19. Nuclear Fission “Splitting the atom”
Break a large nucleus into smaller nuclei
Produces nuclei of lower mass than the reactants

23. Nuclear Chain Reaction
Neutrons from one fission event split further atoms
Only certain isotopes, fissile isotopes, undergo nuclear chain reactions

24. Nuclear Power Plants Provide ~20% U.S. electricity
France >70%
Slow controlled release of energy
Need 2.5–3.5% 235U
Problem with disposal of radioactive waste

26. Nuclear Fusion Reaction takes smaller nuclei and builds larger ones
Also called thermonuclear reactions
Releases tremendous amounts of energy
1 g of H would release same as 20 tons of coal

31. Detection Methods Film Badges- worn by X-ray technicians
Use film exposure to measure radiation exposure of people wearing the badge
Geiger-Muller counters- uses electric impulses carried by gas
Scintillation counters- convert light to an electric signal

32. Half-Life
Time it takes for one-half of the original elements to undergo radioactive decay
Characteristic for each isotope

33. Radioisotopic Dating
Use certain isotopes to estimate the age of various items
235U half-life = 4.5 billion years
Determine age of rock
3H half-life = 12.3 years
Used to date aged wines

34. Carbon-14 Dating 99.9% 12C Produce 14C in upper atmosphere
Half-life of 5730 years
~50,000 y maximum age for dating

35. Half-Life
1. Phosphorus-32 has a half-life of 14.3 days. How many milligrams of phosphorus-32 remain after 28.6 days if you start with 4.0 mg of the isotope?

36. Problems
2. How many milligrams remain of a 15.0mg sample of radium-226 after 6396 years? The half-life of radium-226 is 1599 years.
Isotope name
Original amount
of isotope
Half-Life of
isotope
Number of
half-lives

37. t
3. The half-life of radium-224 is 3.66 days. What was the original mass of radium-224 if g remains after 7.32 days?

39. t
4. The half-life of radon-222 is days. After what time will 25% of a given amount of radon remain?