1. CHAPTER 22 Nuclear Chemistry

2. Types of Radiation
Isotopes - atoms of the same element with the same number of protons but different numbers of neutrons
Radioisotopes – isotope with an unstable nucleus that emits radiation to become a more stable nucleus
Radioactive Decay – spontaneous reaction in which unstable nuclei lose energy in the form of nuclear particles

3. Nuclear Stability Why do atoms decay anyway…
need stable ratio of neutrons to protons
Small atoms are stable with a 1 to 1 ratio of protons to neutrons
As the atomic number increases, atoms tend to have more neutrons than protons with stable ratio increasing to 1 to 1.5
The type of unbalance that is present in the nucleus determines the type of decay.

4. Nuclear Stability

5. Half-life Half-life (t½)
Time required for half the atoms of a radioactive nuclide to decay.
Shorter half-life = less stable.
C. Johannesson

6. Half-life
mf: final mass
mi: initial mass
n: # of half-lives

7. Half-life mf = mi (½)n mf = (25 g)(0.5)12 mf = 0.0061 g WORK:
Fluorine-21 has a half-life of 5.0 seconds. If you start with 25 g of fluorine-21, how many grams would remain after 60.0 s?
WORK:
mf = mi (½)n
mf = (25 g)(0.5)12
mf = g
GIVEN:
t½ = 5.0 s
mi = 25 g
mf = ?
total time = 60.0 s
n = 60.0s ÷ 5.0s
n = 12

8. Types of Nuclear Particles
Alpha particle (α)
Composition: 2 protons, 2 neutrons
Symbol: 4He or α
Charge: +2
Penetrating power: low, stopped by paper or cloth

9. Beta particle (β) Composition: 1 electron Symbol: -1 e Charge: -1
Penetrating power: 100 times greater than alpha, stopped by wood or concrete

10. Gamma ray (γ ) Composition: electromagnetic waves Symbol: γ Charge: 0
Penetrating power: times greater than beta, stopped by lead or 6 feet of concrete

11. Types of Nuclear Decay Numbers must balance!! Alpha Emission parent
nuclide
daughter
nuclide
alpha
particle
Numbers must balance!!

12. Types of Nuclear Decay Beta Emission electron Positron Emission
C. Johannesson

13. Types of Nuclear Decay Electron Capture electron Transmutation
One element becomes another.

14. Fission vs. fusion

15. F ission splitting a nucleus into two or more smaller nuclei
1 g of 235U = 3 tons of coal

16. F ission chain reaction - self-propagating reaction
critical mass - mass required to sustain a chain reaction

17. Fusion combining of two nuclei to form one nucleus of larger mass
thermonuclear reaction – requires temp of 40,000,000 K to sustain
1 g of fusion fuel = 20 tons of coal
occurs naturally in stars
C. Johannesson

18. Fission vs. Fusion 235U is limited fuel is abundant danger of meltdown
toxic waste
thermal pollution
fuel is abundant
no danger of meltdown
no toxic waste
not yet sustainable