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Isotopes Atoms with the same number of protons but different numbers of neutrons Ex) Carbon 12 vs. Carbon 14 These atoms have a different mass Chemically alike because still have the same number of protons Atoms with the same number of protons but different numbers of neutrons Ex) Carbon 12 vs. Carbon 14 These atoms have a different mass Chemically alike because still have the same number of protons

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Isotopes of Hydrogen Hydrogen -1 simply called hydrogen Hydrogen - 2 called deuterium Hydrogen - 3 called tritium Hydrogen -1 simply called hydrogen Hydrogen - 2 called deuterium Hydrogen - 3 called tritium

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Development of AMUs Atomic Mass Units (AMUs) Protons have a mass of 1 amu Neutrona have a mass of 1 amu Electrons have a mass of 0 amu Atomic Mass Units (AMUs) Protons have a mass of 1 amu Neutrona have a mass of 1 amu Electrons have a mass of 0 amu

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Atomic Mass The weighted average mass of the isotopes in a naturally occurring sample of the element Don’t confuse with “mass number” To calculate atomic mass you need 3 pieces of information 1. The number of stable isotopes 2.The mass of each isotope 3.The natural percent abundance of each isotope The weighted average mass of the isotopes in a naturally occurring sample of the element Don’t confuse with “mass number” To calculate atomic mass you need 3 pieces of information 1. The number of stable isotopes 2.The mass of each isotope 3.The natural percent abundance of each isotope

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Atomic Mass Example Problem - Calculate the atomic mass for element X. One isotope has a mass of 10 amus ( 10 X) and is 20% abundant. The other has a mass number of 11 amus ( 11 X) and an abundance of 80%. To solve: Multiply the mass number times the abundance than add them together. Example Problem - Calculate the atomic mass for element X. One isotope has a mass of 10 amus ( 10 X) and is 20% abundant. The other has a mass number of 11 amus ( 11 X) and an abundance of 80%. To solve: Multiply the mass number times the abundance than add them together.

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Atomic Mass 10 x 0.20 = 2.0 11 x 0.80 = 8.8 Add 2.0 + 8.8 = 10.8 The atomic mass of element X is 10.8 amus 10 x 0.20 = 2.0 11 x 0.80 = 8.8 Add 2.0 + 8.8 = 10.8 The atomic mass of element X is 10.8 amus

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Atomic Mass Your turn. Solve: What is the atomic mass of Element Z? The isotopes are 16 Z, 17 Z, 18 Z; with percent abundances of 99.759, 0.037, 0.204. Your turn. Solve: What is the atomic mass of Element Z? The isotopes are 16 Z, 17 Z, 18 Z; with percent abundances of 99.759, 0.037, 0.204.

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Atomic Mass Answer 16 x 0.99759 = 15.961 17 x 0.00037 = 0.0063 18 x 0.00204 = 0.0367 15.961 + 0.0063 + 0.0367 = 16.004 Tha atomic mass of element Z is 16.004 amus Answer 16 x 0.99759 = 15.961 17 x 0.00037 = 0.0063 18 x 0.00204 = 0.0367 15.961 + 0.0063 + 0.0367 = 16.004 Tha atomic mass of element Z is 16.004 amus

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