1. Nuclear Chemistry Chapter 21
Unit 4
Nuclear Chemistry
Chapter 21

2. Background Info
A. Definitions:
nucleons: protons or neutrons
isotopes: ex. U-234 or U-238
nuclide: nucleus with set number of protons and neutrons.
radionuclide: radioactive nucleus
radioisotopes: atoms that are radioactive

3. B. Nuclear stability: -stability belt

4. C. Nuclear Equations & Types of Decay: unstable  electromag
C. Nuclear Equations & Types of Decay: unstable  electromag. + particle + atom radioisotope radiation (stable or unstable)

5. If the atom is unstable, there can be multiple decays or a decay series.

6. He U He II. Types of Decay A. Alpha Decay: (He-4) + 4 2 238 92  23490 He 4 2 +

7.  e I Xe e B. Beta Decay (high energy electron) + or −1 131 53 54 −1 e or I
131 53 Xe 54
 + e −1

8. Beta Decay is: Equal to a neutron changing to a proton n  p + e

9. C. Gamma Radiation (photons) normally not written in the equation. 

10. D. Positron Emission: same size, opposite charge of an electron 1 C 11 6
 B 5 + e 1

11. E. Electron Capture (opposite of beta decay) ex
E. Electron Capture (opposite of beta decay) ex. Rb-81 + electron  Kr-81 Both positron emission and electron capture are equal to a proton changing into a neutron: positron emission: p  n + positron Electron capture: p 1 + e −1
 n

12. III. Rates of Radioactive Decay
Many decay almost instantly (not found in nature)
First order kinetic process
Half life: time required for ½ to react
Each isotope has its own half life
Graph p. 840
Not affected by pressure, temp, etc.

14. A. Dating
C-14: because constant rate of decay, can be used to determine age.
Half life: yrs
C-14 in atmosphere CO2  plants  animals
Ratio of C-12 : C-14
When dead- no longer taking in C…so from ratio at death set and then compare to current, you can find age.
As C-14 decays the ratio changes.
Atmospheric amts of CO2 fairly constant
Check with tree rings & similar ages found

15. Pb-206 : U-238 U-238  Pb-206 (half life: 4.5 x 10 9 yr)
Compare U: Pb ratio
Use for geology

16. B. Calculations based on half lives
Rate = kN
where k = decay constant
N = # of radioactive nuclei
activity = rate at which sample decays
(units: disintegrations/time, becquerel, curie)

18. One can use a device like this Geiger counter to measure the amount of activity present in a radioactive sample.
The ionizing radiation creates ions, which conduct a current that is detected by the instrument.

19. Equation 1
Use if given initial amt, final amt, or time elapsed, and decay constant (or half life)
= -kt Nt N0 ln

20. No = original (bigger #)
Nt = amount after time elapsed (smaller #)
t = time elapsed
k = constant

21. Equation 2 Use if given half life or decay constant = t1/2 0.693 k
t ½ = half life
k = rate constant
= t1/2
0.693 k

22. PRACTICE
A wooden object from an archeological site is subjected to radiocarbon dating. The activity of the sample that is due to 14C is measured to be 11.6 disintegrations per second. The activity of a carbon sample of equal mass from fresh wood is 15.2 disintegrations per second. The half-life of 14C is 5715 yr. What is the age of the archeological sample?

23. Equation 2
= t1/2
0.693 k

24. Equation 1
= -kt Nt N0 ln

25. IV. Biological Effects of Radiation
Radiation is all around us

26. Radiation can: Excite: move e or particles faster
known as non-ionizing radiation
-usually neutralized by water
2. Ionize: removes an electron
known as ionizing radiation – very dangerous

27. A. Ionizing Radiation Damage depends on: Energy of radiation
Exposure time
Internal vs. External
(gamma and x-ray very harmful because small & can get inside body)
Alpha & beta can do more damage if inside body but skin/clothing can block entry because they are larger

29. Cells most likely damaged:
Those that reproduce rapidly
Bone marrow, blood, lymph
More dangerous for children & pregnant women

30. B. Radon Gas Generated as uranium decays in rocks & soil
Chart on p. 857
Noble gas; no smell, taste, or odor
Inhaled & exhaled
Short half life…if decays in lungs then an alpha particle (large) is released
Becomes Po-218 that also releases an alpha (and has a short half life)

31. C. Cancer treatment High energy radiation
Lots of energy in a little time (short half lives)
Administered as:
Seeds – coated radioactive material inserted
Ingested – (I-131 to thyroid) some chemicals go to specific areas in the body
Co-60 shot into tumor
Also damages healthy cells - side effects

33. V. Energy and Nuclear Chemistry
E = mc2
Extremely large amounts of energy
Fission: (nuclear power & weapons)

34. Fusion: (reaction on the sun)
H H-3  He + Energy
ideal for energy (less harmful products) but requires much energy to get rxn started.