Nuclear Chemistry

THE NUCLEAR ATOM

RadioactivityNot all atoms are stable.Unstable atoms break down and give off

energy to become more stable.These atoms are referred to as

RADIOISOTOPES.The energy and particles that are given off

when radioisotopes break down are called RADIATION.

Radioisotopes break down in a series of nuclear reactions known as NUCLEAR DECAY.

Nuclear Decay3 Types of Radiation

AlphaBetaGamma

Type of radiation emitted is determined by the neutron to proton ratio.

Stable nuclei have a ratio that is found within the BAND OF STABILITY. (see graph p. 803)Small atoms have a ratio of approx. 1Heavy atoms have a ratio of approx. 1.5

Alpha RadiationAlpha Decay occurs when the nucleus is

too big.In alpha decay, an alpha particle or helium

nucleus is emitted. (42 He)

2 protons2 neutrons0 electrons

22688 Ra 222

86 Rn + 42 He

Beta RadiationBeta Decay occurs when there are too

many neutrons relative to protons.In beta decay, a neutron turns into a

proton by giving off a beta particle or electron. (0

-1e)n0 p+ + e-

6629 Cu 66

30 Zn + 0-1e

Gamma RadiationGamma radiation or gamma rays are given

off during alpha or beta decay.Gamma rays have no mass and no charge.

(γ)Therefore, they do not alter the number of

protons or neutrons in the nucleus.

22688 Ra 222

86 Rn + 42 He + γ

Decay Equations Practice…Write the decay equation.Uranium-238 undergoes α decay.

Bismuth-210 undergoes β decay.

Thorium-230 undergoes α and γ decay.

Lead-214 undergoes β and γ decay.

Nuclear Equation Practice1. 63Cu + 2H → 21n + ____2. 44Ca + 1H → 44Sc + ____3. 9Be + 4He → 12C + ____4. 31P + 2H → 32P + ____5. 37Cl + ____ → 35S + 4He6. ____ → 237Np + α7. 214Pb → β + ____

Damage from RadiationAlpha, beta, and

gamma can ALL cause damage.

However, they differ in the degree and how easily you are protected.

Half-Life: rate of decayAll radioactive decay occurs at a steady rate.The rate is measured in terms of how long it takes

for ½ of the substance to decay. (half-life)Each substance has its own half-life.

Carbon-14 5.73 x 103 yearsRadon-222 3.8 daysHelium-6 0.802 seconds

Half-Life ProblemsWhat is the half life of the

graphed material?

What mass of radioisotope will remain after 9.0 hours?

How long will it take for only ¾ of the radioisotope to decay?

How long for only 3.125 grams to remain?

Half Life Practice1. Initial mass = 64g 4 half lives Final

mass = ?2. Initial mass = 32g t = 8.0yr ½ life =

2.0yr Final mass = ?3. Initial mass = 128g t = 5d ½ life

= 24hr Final mass = ?4. Initial mass = 400.0g Final mass =

50.0g ½ life = 13.6d t = ?5. Initial mass = 1.0000g Final mass =

0.15625g ½ life = 2325yr t=?

Other Radioactive ReactionsFission and FusionFission is the SPLITTING of atoms.

…what happens in a nuclear reactorFusion is the COMBINING of atoms.

…what happens on the sun

Both result in the release of large amounts of energy.

FissionFission occurs when

certain nuclei are bombarded with neutrons.When the atom splits, it

releases additional neutrons which cause other atoms to split creating a chain reaction.

FusionFusion occurs when

small nuclei combine to create larger nuclei.

Fusion creates MORE energy than fission.

Neutrons, positrons, or electrons may be given off in a fusion reaction.

Deuterium (2H) + Tritium(3H) Helium (4He) + neutron (1n)

Pros and ConsFission

Pro - relatively easy to control

Con - produce radioactive wastes

FusionPro - produce little

radioactive wastes

Con - difficult to initiate and control

Uses of Radioactivity???