CHAPTER 22 Nuclear Chemistry. Types of Radiation Isotopes - atoms of the same element with the same...
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Transcript of CHAPTER 22 Nuclear Chemistry. Types of Radiation Isotopes - atoms of the same element with the same...
CHAPTER 22Nuclear Chemistry
CHAPTER 22Nuclear Chemistry
Types of RadiationTypes of RadiationTypes of RadiationTypes 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
Nuclear StabilityNuclear StabilityNuclear StabilityNuclear 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.
Nuclear StabilityNuclear StabilityNuclear StabilityNuclear Stability
C. Johannesson
Half-lifeHalf-lifeHalf-lifeHalf-lifeHalf-life (t½)
Time required for half the atoms of a radioactive nuclide to decay.
Shorter half-life = less stable.
Half-lifeHalf-lifeHalf-lifeHalf-life
nif mm )( 2
1
mf: final massmi: initial massn: # of half-lives
Half-lifeHalf-lifeHalf-lifeHalf-life 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?
GIVEN:
t½ = 5.0 s
mi = 25 g
mf = ?
total time = 60.0 s
n = 60.0s ÷ 5.0s
n = 12
WORK:
mf = mi (½)n
mf = (25 g)(0.5)12
mf = 0.0061 g
Types of Nuclear Types of Nuclear ParticlesParticles
Types of Nuclear Types of Nuclear ParticlesParticles
Alpha particle (α)
Composition: 2 protons, 2 neutronsSymbol: 4He or αCharge: +2Penetrating power: low, stopped by
paper or cloth
Beta particle (β)
Composition: 1 electronSymbol: -1 e
Charge: -1Penetrating power: 100 times
greater than alpha, stopped by wood or concrete
Gamma ray (γ )
Composition: electromagnetic waves
Symbol: γCharge: 0Penetrating power: 1000 times
greater than beta, stopped by lead or 6 feet of concrete
Types of Nuclear DecayTypes of Nuclear DecayTypes of Nuclear DecayTypes of Nuclear Decay
Alpha Emission
He Th U 42
23490
23892
parentnuclide
daughternuclide
alphaparticle
Numbers must balance!!
C. Johannesson
Types of Nuclear DecayTypes of Nuclear DecayTypes of Nuclear DecayTypes of Nuclear Decay
Beta Emission
e Xe I 0-1
13154
13153
electronPositron Emission
e Ar K 01
3818
3819
positron
Types of Nuclear DecayTypes of Nuclear DecayTypes of Nuclear DecayTypes of Nuclear Decay
Electron Capture
Pd e Ag 10646
0-1
10647
electron
Transmutation One element becomes another.
Fission vs. fusionFission vs. fusion
FF issionissionFF issionission
splitting a nucleus into two or more smaller nuclei
1 g of 235U = 3 tons of coal
U23592
FF issionissionFF issionissionchain reaction - self-propagating reactioncritical mass -
mass required to sustain a chain reaction
C. Johannesson
FusionFusionFusionFusioncombining of two nuclei to form one nucleus of larger mass thermonuclear reaction – requires temp of 40,000,000 K to sustain1 g of fusion fuel =
20 tons of coaloccurs naturally in
stars
HH 31
21
Fission vs. FusionFission vs. FusionFission vs. FusionFission vs. Fusion
235U is limited danger of meltdown toxic waste thermal pollution
fuel is abundant no danger of meltdown no toxic waste not yet sustainable
FISSION
FUSION