CHEM 108 1st Edition Lecture 36Chapter 21: Nuclear ChemistryNuclear Chemistry: - The study of reactions that involve changes in the nuclei of atoms. - Radioactive Decay: The spontaneous disintegration of unstable particles accompanied by the release of radiation. o Radioactive decay follows first-order kinetics.o Chemical reaction: valence shell electrons usually involved o Nuclear reaction: nucleus usually involved o Symbols: mass number, atomic number, element symbol o Symbols: proton, neutron, electron, positron, gamma ray (photon) o Nuclear reactions: mass number and atomic number must balanceo Activity units: Becquerel = 1 disintegration/sec o Curie (Ci) = 3.7 x 1010 disintegrations/secSymbols for particles:Radioactive decay: - Alpha emission: emission of helium nucleus - Net result: atomic number decreases by 2 and mass decreases by 4 o22688Ra -->22286Rn + 42He- Beta emission: emission of electron from the nucleus - Net result: atomic number increases by 1o146C -->147N + 0-1e- Positron emission: emission of positively-charged electron from a nucleus - Net: atomic number decreases by 1 o9543Tc -->9542Mo + 0 1e- Electron capture reaction of proton and electron - Net result: atomic number decreases by 1 o4019K + 0-1e -->4018Ar- Gamma emission: emission of photon from nucleus - Net result: energy of nucleus decreases o99m43Tc -->9943Tc + 00γ- NT/NO= 0.5npercentage of element left after n number of half-lives.o NT= number of days o NO= number of days the half-life equals o n= number of half-lives Balancing nuclear equations: - Balance masses on left/right: 1 = 1 + 0 - Balance charges on left/right: 0 = 1 + −1Solar Fusion:- Positron: Particle with mass of an electron but with a positive charge. - Antimatter: Particles that are charge opposites of normal subatomic particles (e.g., electron / positron). -11H + 11H 21H + 01e (positron)- Collision of matter/antimatter particles results in annihilation; all mass converted to energy in the form of γ-rays:o0-1 + 01 2γNuclear Binding Energies:- Binding Energy (BE): The energy released when nucleons combine to form a nucleus. • Depends on “mass defect.” - Mass Defect (Δm): Difference between the mass (in kg) of a stable nucleus and the individual nucleons that comprise it. - E = (Δm)c2 (Note: Joule = (kg∙m2 )/s2 )- 1 amu =1.66054 × 10−27
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