RADIOACTIVITY, NUCLEAR ENERGY, SOLAR ENERGY Introduction – Part 1 Nuclear Energy or Fission – Part 2 Solar Energy or Fusion – Part 3

Nuclear Chemistry The study of the properties and changes (rxns) that take place in atomic nuclei. Isotopes have the same Z but different # of neutrons; i.e. different mass number Carbon has 13 isotopes C-12 has 6 p +, 6 n 0 and 6 e - ; stable C-13 has 6 p +, 7 n 0 and 6 e - ; stable C-14 has 6 p +, 8 n 0 and 6 e - ; unstable

Radioactive Elements Elements that are unstable and that decompose spontaneously. All elements have at least one radioactive isotope. Elements with Z > 83 are radioactive. The decomposition products are –other elements - stable or radioactive –high energy particles – alpha, beta, gamma During these decompositions, mass and charge must be conserved.

Alpha Particles (α) Review definition of isotope, Z, mass number, structure of atom α = nucleus of He or 4 2 He with charge = +2 and mass number = 4 = 2 n p + Ex 17.2a Pu  U He Ex 17.2c Au  Ir He State Z (#p + ), #n 0 for each species in eqn. Note that Z of product element decreases

Beta Particles (β) β = electron with charge = -1 and negligible mass Produced when neutron splits –neutron  proton + electron Ex 17.3a 14 6 C  14 7 N e Ex 17.3c Mo  Tc e State Z (#p + ), #n 0, #e -1 Note that Z of product element increases

Gamma Emission (γ) γ = gamma ray = light or photon with no mass and no charge High energy photons

Summary ParticleSymbolChange in Z Change in mass number Change in #n 0 Alphaα, 4 2 He Betaβ, 0 -1 e+10 Gammaγ, 0 0 γ000

What α, β, γ Emissions Do These radioactive byproducts are emitted at very high energies. These energies can be high enough to –break chemical bonds and ionize atoms and molecules. –produce free radicals that can damage DNA, proteins –damage tissue if the radioactive element is ingested –cause cell mutations –kill cells

Radioactive Decay As mentioned before,radioactive atoms are unstable and decay spontaneously. Some atoms decay over a long period of time (billions of years) and others over a short period of time (fractions of seconds) One radioactive atom may decay to another which then decays to another (Fig 17.5)

Radioisotope Half-Life, τ 1/2 Half-life is the time it takes for half of the atoms in a radioactive sample to decay. The longer the half-life, the longer the radioactive isotope exists and the longer its potential danger exists. Prob 17-43: After 6 hr, 25 mg remain. After 12 hr, 12.5 mg remain. After 18 hr, 6.25 mg remain. After 24 hr, mg remain. After 48 hr, 0.20 mg remain. Fig 17.4

Uses of Radioisotopes Radio isotope SymbolProdHalf-lifeUse Tritium 31H31Hβ12.33 yrBiochem tracer C Cβ5730 yrC-dating P Pβ14 dyLeukemia therapy Co Coβ5.27 yrCancer therapy I Iγ13.27 hrThyroid therapy

Nuclear and Chemical Rxns A Comparison Reactant atoms ≠ product atoms Conservation of atom identities Diff isotopes may have diff nuclear properties Diff isotopes may chem properties Rate of nuclear rxn ≠ f(T, P, catalyst) Rate of chem rxn = f(T, P, catalyst) Nuclear rxn ≠ f(atom’s environment, phase) Chem rxn = f(atom’s environment, phase) Energy changes: 1 g U- 235 releases 8.2E+7 kJ 1 g methane burns to produce 56 kJ