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NUCLEAR CHEMISTRY. By: Stephanie Chen and Stephanie Ng. Radioactivity. One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie (1876-1934). - PowerPoint PPT Presentation

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  • NUCLEAR CHEMISTRYBy: Stephanie Chen and Stephanie Ng

  • RadioactivityOne of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie (1876-1934). She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.

  • Nuclear Reactions vs. Normal Chemical ChangesNuclear reactions involve the nucleusThe nucleus opens, and protons and neutrons are rearrangedThe opening of the nucleus releases a tremendous amount of energy that holds the nucleus together called binding energyNormal Chemical Reactions involve electrons, not protons and neutrons

  • 23.1

  • Types of Radiation Alpha () a positively charged (+2) helium isotope - we usually ignore the charge because it involves electrons, not protons and neutronsBeta () an electronGamma () pure energy; called a ray rather than a particle

  • Other Nuclear Particles Neutron Positron a positive electronProton usually referred to as hydrogen-1Any other elemental isotope

  • Penetrating Ability

  • Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutronsAZ11100-10+14223.1

  • 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 + 2x023.1

  • 212Po decays by alpha emission. Write the balanced nuclear equation for the decay of 212Po.212 = 4 + AA = 20884 = 2 + ZZ = 8223.1

  • Nuclear Stability and Radioactive DecayBeta decayDecrease # of neutrons by 1Increase # of protons by 1Positron decayIncrease # of neutrons by 1Decrease # of protons by 123.2

  • Electron capture decayIncrease # of neutrons by 1Decrease # of protons by 1Nuclear Stability and Radioactive DecayAlpha decayDecrease # of neutrons by 2Decrease # of protons by 2Spontaneous fission23.2

  • Learning CheckWhat radioactive isotope is produced in the following bombardment of boron?10B + 4He 13N + 1n 5 2 7 0

  • Write Nuclear Equations!Write the nuclear equation for the beta emitter Co-60.60Co0e+60Ni 27 -128

  • Artificial Nuclear ReactionsNew elements or new isotopes of known elements are produced by bombarding an atom with a subatomic particle such as a proton or neutron -- or even a much heavier particle such as 4He and 11B.Reactions using neutrons are called g reactions because a g ray is usually emitted.Radioisotopes used in medicine are often made by g reactions.

  • Artificial Nuclear ReactionsExample of a g reaction is production of radioactive 31P for use in studies of P uptake in the body.3115P + 10n ---> 3215P + g

  • Transuranium ElementsElements beyond 92 (transuranium) made starting with an g reaction 23892U + 10n ---> 23992U + g23992U ---> 23993Np + 0-1b 23993Np ---> 23994Pu + 0-1b

  • 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 radioactive23.2

  • Band of Stability and Radioactive Decay

  • Stability of Nuclei Out of > 300 stable isotopes:EvenOddOddEvenZN15752505

  • Half-LifeHALF-LIFE is the time that it takes for 1/2 a sample to decompose.The rate of a nuclear transformation depends only on the reactant concentration.

  • Half-Life

    Decay of 20.0 mg of 15O. What remains after 3 half-lives? After 5 half-lives?

  • Kinetics of Radioactive DecayFor each duration (half-life), one half of the substance decomposes.For example: Ra-234 has a half-life of 3.6 days If you start with 50 grams of Ra-234

    After 3.6 days > 25 gramsAfter 7.2 days > 12.5 gramsAfter 10.8 days > 6.25 grams

  • Kinetics of Radioactive Decayrate = lNN = N0e(-lt)lnN = lnN0 - ltN = the number of atoms at time tN0 = the number of atoms at time t = 0l is the decay constant (sometimes called k)23.3 k =

  • Kinetics of Radioactive Decay[N] = [N]0exp(-lt)ln[N] = ln[N]0 - lt23.3

  • Radiocarbon Datingt = 5730 yearsUranium-238 Datingt = 4.51 x 109 years23.3

  • Learning Check! The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 31 hours?

  • Nuclear FissionFission is the splitting of atomsThese are usually very large, so that they are not as stableFission chain has three general steps:1. Initiation. Reaction of a single atom starts the chain (e.g., 235U + neutron)2. Propagation. 236U fission releases neutrons that initiate other fissions3. Termination.

  • Nuclear Fission

  • Nuclear Fission23.5Energy = [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

  • Representation of a fission process.

  • Mass DefectSome of the mass can be converted into energyShown by a very famous equation! E=mc2

    EnergyMassSpeed of light

  • 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 J23.2

  • Nuclear binding energy per nucleon vs Mass number23.2

  • Nuclear Fission23.5Nuclear 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.

  • Nuclear FusionFusion small nuclei combine

    2H + 3H 4He + 1n + 1 1 2 0

    Occurs in the sun and other stars

    Energy

  • Nuclear FusionFusion Excessive heat can not be containedAttempts at cold fusion have FAILED.Hot fusion is difficult to contain