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Key questions: What are isotopes? What are the types of isotopes? How do we measure isotopes? How do we express measurements of isotopes? What is isotope fractionation and how do we express it? What is equilibrium isotope fractionation? What is kinetic isotope fractionation? What is Raleigh distillation? What are some applications of stable isotopes? Isotopes of Elements Atomic Number = # Protons = defines which element and its chemistry Atomic Weight = protons + neutrons = referred to as isotopes Different elements have different numbers of neutrons and thus atomic weights. Example: Carbon can exist as 12C, 13C, 14C How many protons and neutrons in each of the C isotopes? 12C = 6P, 6N 13C = 6P, 7N 14C = 6P, 8N 1 chemical, many isotopes! Where do Isotopes come from? In the beginning (Big Bang), light elements of H and He were formed (and a little bit of Li) Nuclear reactions (ie: fusion) in stars created the remaining elements (and are still creating), some of which have since decayed to more stable elements There are 92 naturally occurring elements – some are stable, some are not Types of Isotopes Isotopes can be categorized into 2 categories: Stable isotopes – Isotopes that do not decay over the timescale of earth history (4.5 billion years) Radioactive isotopes – Isotopes that spontaneously convert into other nuclei at a discernable rate The chart of the nuclides (protons versus neutrons) for elements 1 (Hydrogen) through 12 (Magnesium). Valley of Stability Most elements have more than one stable isotope. 1:1 line b decay X X a decay Number of neutrons tends to be greater than the number of protons
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