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Published byMaurice Terry Modified over 6 years ago
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4.2 Periodic Table Squares and Average Atomic Mass
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Element Name Atomic Number Chemical Symbol Atomic Mass
Atomic Number: Number of Protons Atomic Mass: Average mass based on the abundance of an element’s isotopes Chemical Symbol Atomic Mass
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Mass Number = # of protons + # of neutrons
Learning Check Based on the atomic number and mass number, find the number of neutrons in an oxygen atom. (Hint: assume the atomic mass is 16) Answer: 8 neutrons
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Isotopes When the NUMBER OF NEUTRONS changes in an atom.
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Average Atomic Mass Represents the average mass of an element based on its isotopes. UNITS are amu (atomic mass units) Average Atomic Mass = (% abundance x mass) + (% abundance x mass) + (% abundance x mass) …..
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Let’s try this together
Lithium’s isotopes have an abundance ratio of 7.5% of Lithium-6, and 92.5% of Lithium-7. What is Lithium’s average atomic mass? Answer: (% abundance x mass) + (% abundance x mass) = average atomic mass (0.075 x 6) + (0.925 x 7) = amu
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Try this on your own Iron’s isotopes have an abundance ratio of 15% Fe-55, and 85% Fe-56. What is iron’s average atomic mass? (.15 x 55) + (.85 x 56) = amu
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One more for good luck Chlorine’s isotopes have an abundance ratio of % Cl-35 and 24.22% of Cl-37. What is the average atomic mass of Chlorine? (.7578 x 35) + (.2422 x 37) = amu
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