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Average Atomic Mass Due Monday Oct 14, 2013 http://tinyurl.com/md228mj

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Objective Calculate the average atomic mass for an element

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Average Atomic Mass The weighted average mass of all the isotopes found in nature for that element.

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Average Atomic Mass Measured in atomic mass units (amu)

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Mass Spectrometer Instrument that determines the percentages and individual masses of each isotope

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Calculation The average atomic mass is calculated by the percent of each isotope’s mass [(mass of isotope) (%abundance)] + [(mass of isotope) (%abundance)] + [(mass of isotope) (%abundance)] …

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Practice Problem 1 Boron has two isotopes: Boron-10 and Boron-11. In nature 19% of Boron is Boron- 10, and 81% is Boron-11.

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Practice Problem 2 A new element, Tyserium (Ty), has recently been discovered on Mars and consists of two isotopes. One isotope has a mass of 331 amu and is 35.0 % abundant. The other isotope is 339 amu and is 65.0 % abundant. What is the mass of Ty as it appears on the periodic table?

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Logic Problem #1 Copper has an average atomic mass of 63.546 amu and only exists as Copper- 63 and Copper-65. What is the isotopic mass of the most common isotope of Copper?

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Logic Problem #2 The relative atomic mass of chlorine is 35.5 amu. What does this tell you about the relative abundance of the two naturally occurring isotopes of chlorine, Chlorine-35 and Chlorine-37.

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Check Yourself! Make sure your calculated average atomic mass is within the range of the given mass numbers – X-230, X-235, X-240 Rationalize your results – 90% of X-230, 5% of X-235, 5% of X-240 Check your answers on the periodic table

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Questions? If you have any questions, jot them down!

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