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