Nuclear ChemistryChapter 23

Nuclear StabilityCertain numbers of neutrons and protons are extra stablen or p = 2, 8, 20, 50, 82 and 126Like extra stable numbers of electrons in noble gases (e- = 2, 10, 18, 36, 54 and 86)Nuclei with even numbers of both protons and neutrons are more stable than those with odd numbers of neutron and protonsAll isotopes of the elements with atomic numbers higher than 83 are radioactiveAll isotopes of Tc and Pm are radioactive

Atomic number (Z) = number of protons in nucleus (element symbols) = charge (particles) Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutronsAZ11100-10+142Other relevant particles of interest:Gamma photonneutrinoAnti-neutrino

Balancing Nuclear EquationsConserve mass number (A). The sum of protons plus neutrons in the products must equal the sum of protons plus neutrons in the reactants.235 + 1 = 138 + 96 + 2x1Conserve atomic number (Z) or nuclear charge. The sum of nuclear charges in the products must equal the sum of nuclear charges in the reactants.92 + 0 = 55 + 37 + 2x0

212Po decays by alpha emission. Write the balanced nuclear equation for the decay of 212Po.212 = 4 + AA = 20884 = 2 + ZZ = 82?

Nuclear Stability and Radioactive DecayBeta decayDecrease # of neutrons by 1Increase # of protons by 1Positron decayIncrease # of neutrons by 1Decrease # of protons by 1

Electron capture decayIncrease # of neutrons by 1Decrease # of protons by 1Nuclear Stability and Radioactive DecayAlpha decayDecrease # of neutrons by 2Decrease # of protons by 2Spontaneous fission

Nuclear binding energy (BE) is the energy required to break up a nucleus into its component protons and neutrons.BE = 9 x (p mass) + 10 x (n mass) 19F massE = mc2BE (amu) = 9 x 1.007825 + 10 x 1.008665 18.9984BE = 0.1587 amu1 amu = 1.49 x 10-10 JBE = 2.37 x 10-11J= 1.25 x 10-12 J

Nuclear binding energy per nucleon vs Mass number

Kinetics of Radioactive Decayrate = lNN = the number of atoms at time tN0 = the number of atoms at time t = 0l is the decay constantFirst Order Equations:

Kinetics of Radioactive Decay[N] = [N]0exp(-lt)ln[N] = ln[N]0 - lt

Radiocarbon Datingt = 5730 yearsUranium-238 Datingt = 4.51 x 109 years

Nuclear Transmutation

Nuclear Transmutation19401940194419441949195019521952195519561961196619701984198119841982199419942002110111112 Darmstadtium Ds Roentgenium Rg Copernicium Cn

Nuclear FissionEnergy = [mass 235U + mass n (mass 90Sr + mass 143Xe + 3 x mass n )] x c2Energy = 3.3 x 10-11J per 235U= 2.0 x 1013 J per mole 235UCombustion of 1 ton of coal = 5 x 107 J

Nuclear FissionRepresentative fission reaction

Nuclear FissionNuclear chain reaction is a self-sustaining sequence of nuclear fission reactions.The minimum mass of fissionable material required to generate a self-sustaining nuclear chain reaction is the critical mass.

Schematic Diagram of a Nuclear Reactor

Annual Waste ProductionNuclear Fission

Nuclear FissionHazards of the radioactivities in spent fuel compared to uranium oreFrom Science, Society and Americas Nuclear Waste, DOE/RW-0361 TG

Chemistry In Action: Natures Own Fission ReactorNatural Uranium0.7202 % U-235 99.2798% U-238Measured at Oklo0.7171 % U-235

Nuclear FusionFusion ReactionEnergy Released6.3 x 10-13 J2.8 x 10-12 J3.6 x 10-12 JTokamak magnetic plasma confinement

Radioisotopes in Medicine1 out of every 3 hospital patients will undergo a nuclear medicine procedure24Na, t = 14.8 hr, b emitter, blood-flow tracer131I, t = 14.8 hr, b emitter, thyroid gland activity123I, t = 13.3 hr, g-ray emitter, brain imaging18F, t = 1.8 hr, b+ emitter, positron emission tomography99mTc, t = 6 hr, g-ray emitter, imaging agentBrain images with 123I-labeled compound

Radioisotopes in MedicineResearch production of 99MoCommercial production of 99Mot = 66 hourst = 6 hours

Geiger-Mller Counter

Biological Effects of RadiationRadiation absorbed dose (rad)1 rad = 1 x 10-5 J/g of materialRoentgen equivalent for man (rem)1 rem = 1 rad x QQuality Factorg-ray = 1b = 1a = 20

Chemistry In Action: Food Irradiation

DosageEffectUp to 100 kiloradInhibits sprouting of potatoes, onions, garlics. Inactivates trichinae in pork. Kills or prevents insects from reproducing in grains, fruits, and vegetables.100 1000 kilorads Delays spoilage of meat poultry and fish. Reduces salmonella. Extends shelf life of some fruit.1000 to 10,000 kiloradsSterilizes meat, poultry and fish. Kills insects and microorganisms in spices and seasoning.