Nuclear ChemistryNuclear Chemistry

Isotopes-ReviewIsotopes-Review

► Isotopes are atoms of the same Isotopes are atoms of the same element element that have the same # of that have the same # of protonsprotons but different # of but different # of neutronsneutrons or or mass.mass.

XXAtomic mass

Atomic number

► When the size and mass of the nucleus becomes When the size and mass of the nucleus becomes large (greater than atomic #83), the element is large (greater than atomic #83), the element is known to be known to be radioactive (unstable)radioactive (unstable) because it because it decays.decays.

► Examples:Examples:Pu-239 (94 protons), U-238 (92 protons)Pu-239 (94 protons), U-238 (92 protons)

► When the ratio of neutrons to protons is When the ratio of neutrons to protons is greater greater than 1:1 (for light nuclei)than 1:1 (for light nuclei) , the element is also , the element is also radioactive.radioactive.

► Examples:Examples:Carbon-14, Lithium-7Carbon-14, Lithium-7

Natural radioactivityNatural radioactivity► Occurs when nuclei are Occurs when nuclei are

unstable.unstable.► For any element, an isotope that For any element, an isotope that

is unstable is called a is unstable is called a radioisotoperadioisotope..

Particles Emitted Particles Emitted

►When a nucleus decays, it When a nucleus decays, it emits emits particles. particles.

Particle Mass Charge Symbol Penetrating Power

Alpha 4 amu 2+ , 24He Low

Beta 0 amu 1- -, -10e Moderate

Positron 0 amu 1+ + 10e  Moderate

Gamma 0 amu none , 00 High

Alpha DecayAlpha Decay

► when an unstable nucleus emits an when an unstable nucleus emits an alpha particle, this is called alpha alpha particle, this is called alpha decay. decay.

Beta DecayBeta Decay

►When an unstable nucleus emits a When an unstable nucleus emits a beta particle, this is called a beta beta particle, this is called a beta decay.decay.

Positron EmissionPositron Emission

►When an unstable nucleus emits a When an unstable nucleus emits a positron, it is called positron emissionpositron, it is called positron emission

Writing Nuclear EquationsWriting Nuclear Equations

►Obeys laws of Obeys laws of conservationconservation of of mass mass andand chargecharge. .

Natural TransmutationNatural Transmutation

►Begins with one nucleus that Begins with one nucleus that spontaneously decays.spontaneously decays.

***Always has ONE REACTANT.***Always has ONE REACTANT.

Artificial Transmutation Artificial Transmutation

►Bombardment ofBombardment of the nucleus with the nucleus with high energy particles.high energy particles.

***Always has TWO REACTANTS.***Always has TWO REACTANTS.

Fission Reactions Fission Reactions

► Involve the Involve the splitting of a heavy splitting of a heavy nucleusnucleus to produce to produce lighter nucleilighter nuclei..

Fission reactions produce/capture neutrons. They can become involved in another fission reaction.

If the number of If the number of neutronsneutrons released is released is not controlled a not controlled a chain reactionchain reaction will will occur.occur.

This is the type of reaction used in This is the type of reaction used in nuclearnuclear bombsbombs. .

Fusion ReactionsFusion Reactions

► Involves Involves the combining of the combining of nucleinuclei to produce to produce heavier heavier onesones..

In fission and fusion reactions, there In fission and fusion reactions, there appears to be a loss of mass. appears to be a loss of mass. However, this mass has been However, this mass has been converted to energy by the equationconverted to energy by the equation

E = mcE = mc22

Nuclear vs. Chemical Nuclear vs. Chemical Fission vs. Fusion Fission vs. Fusion

The energy of nuclear reactions is much The energy of nuclear reactions is much greatergreater than the energy associated than the energy associated with chemical reactions. with chemical reactions.

The energy of The energy of fissionfission is greater than is greater than the energy of the energy of fusionfusion..

Half-LifeHalf-Life

►Radioactive substances decay at a rate Radioactive substances decay at a rate that is that is not dependentnot dependent on on temperature, pressure, or temperature, pressure, or concentrationconcentration..

►Half-life is Half-life is the time it takes for half the time it takes for half the atoms in a given sample of an the atoms in a given sample of an element to decay.element to decay.

►See Table N for half-lives and modes.See Table N for half-lives and modes.

Uses of RadioactivityUses of Radioactivity

►DatingDating C-14 used to C-14 used to date organic remains; date organic remains; U-238:Pb-206 for U-238:Pb-206 for mineralsminerals

Uses continuedUses continued

►Chemical tracersChemical tracers can follow the path can follow the path of a material (ex: fertilizer)of a material (ex: fertilizer)

► Industrial applicationsIndustrial applications can test can test thickness or strength of materialsthickness or strength of materials

Uses continuedUses continued

►Medical applicationsMedical applications must have short must have short half-life and quickly eliminated from half-life and quickly eliminated from body, I-131 thyroid, Tc-99/Co-60 body, I-131 thyroid, Tc-99/Co-60 cancercancer

Dangers of Radioactivity Dangers of Radioactivity

►Damage to Damage to tissuetissue►Gene Gene mutationmutation