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Isotopes • Have same chemical proper/es
– (determined by # electrons)
• All isotopes of an element have the same atomic number (#P)
Atomic Mass of an Element • An average of the masses of all naturally occurring isotopes mul/plied by the abundance of each isotope as a decimal
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Calculating average atomic mass for Carbon
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Uses of Isotopes • Food irradia/on • Archeological da/ng • Smoke detectors • Radioac/ve tracers
Calcula/ng Average Weighted Atomic Mass
• Must know: – 1) number of isotopes – 2) mass of each isotope – 3) natural percent abundance of each isotope
• Calcula/on: – Mul/ply mass of each isotope by natural abundance, express as decimal and add products
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Radioac/ve Isotopes & Nuclear Chemistry
• Study of the produc/on and use of radioac/ve sources for medicine, industry, spacecraP
What causes atoms to be radioac/ve? • An atom with an unstable nucleus, where the nucleus has an excess of internal energy (too many neutrons or protons)
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Radioac/ve Decay • The process when an unstable nucleus emits radia/on (disintegrates), turning into new element
• May eject neutrons or protons • Convert one subatomic par/cle to another • Releasing energy (gamma rays)
Radioac/ve Isotopes (radioisotope) • Unstable nuclei, dissipate excess energy by emiUng radia/on in the form of alpha, beta, and gamma rays
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Radiocarbon Da/ng • C-‐14 Da/ng: Can determine age of biological sample (wood, bones, teeth)
Da*ng Organic Material Using Carbon 14 • Ra*o of Carbon 14 (radioac/ve) to carbon 12 is used to date remains of living things
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Half life
Half life: 0
Half life: 1
Half life: 2
Linear
Exponential
• The half life is the amount of time needed for half the parent isotope to decay to the daughter isotope
By measuring how many half-lives have passed since rock was formed, age of rock is determined.
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The Half-‐life of 14C is 5,730 years.
Using radiometric da/ng: Oldest Rocks on Earth
• Oldest rocks on Earth are the Acasta Gniess of northern Canada • 4030 million years old
© NASA
Acasta Gneiss
Zircon mineral