In the beginning….The Big Bang “quark soup” nuclei of H and HeToday’s topic:Nucleosynthesis and the origin of the chemical elements(all in ~13.8 s)CNO cycleProton-proton chain orHydrogen “burning”Nucleosynthesis —The origin of the chemical elements24HeStandard notation2Atomic numberMass number4Element symbolHeHe2Atomic numberMass number4(# of protonsand neutrons)(# of protons)Atomic weight is the sum of the masses of all natural isotopes of that element weighted based on their abundanceThe atomic weightyou see on the periodic tableO8Atomic numberMass number16(# of protonsand neutrons)(# of protons)The most commonisotope of oxygen isoxygen-16O8Atomic numberMass number18(# of protonsand neutrons)(# of protons)Isotopes have a different number ofneutrons so their mass number will bedifferent, but the atomic number of anelement is always the sameCNO cycleProton-proton chain orHydrogen “burning”Nucleosynthesis —The origin of the chemical elementsHelium burning —The triple-alpha processKey to synthesis of allelements beyond HeNuclei of higher atomic number than C are produced by fusing alpha particles (He)…but the heaviest atom produced this way is Nickel-56Neutron captureThis process is responsible for elements withatomic number > 26 (Fe)S-process(Neutron-capture)Beta decayβ β_(electron) or (positron) +Stars’ nuclear firesDiameter of the starexpands while the core contracts leading to “giant” starsHydrogen burningReddwarfsBluegiantsRedgiantsBetelgeuse and RigelWhitedwarfsmostcommonThe Sun in 5 GaHydrogen burningReddwarfsBluegiantsRedgiantsBetelgeuse and RigelWhitedwarfsmostcommonThe Sun in 5 GaWhen a mid- toheavy-weight stardies, a supernovaexplosion ejectsthe outer layers of the star (and the elements therein) into the universe creating the rawmaterial for planetsPlanets form bygravitationalcollapse and/oraccretionAbundances of elementsin the solar system• H and He most abundant (90-95% H, 5-10% He)• Abundances of first 50 elements decreases exponentially• Even atomic numbers are more abundantMost abundantMass number # protons # neutronsThe most “even” isotopes aremore abundantThe abundance of the elements is related to their nuclear propertiesrather than their chemical properties…Abundances of elementsin the solar system• Elements with Z ≥ 83 have no stable isotopes but occur naturally because they are daughters of long-lived radio-isotopes of U and ThNo stable isotopesPeriods are numbered based on the first quantum number of the orbitals that are being filled with increasing atomic number1s2s, 2p3s, 3p4s, 3d, 4p5s, 4d, 5p6s, 4f, 5d, 6petc….7s, 5f, 6d, 7pElectron cloudsororbitals1s2s, 2p3s, 3p4s, 3d, 4p5s, 4d, 5p6s, 4f, 5d, 6p7s, 5f, 6d,
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