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Average Atomic Mass

Average Atomic Mass. Average Atomic Mass. atomic masses reported in periodic table represent: weighted average of masses of all naturally occurring isotopes of an element. Weighted Average:Test Grades. suppose have : 1 test of 0% and 9 tests of 90%

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Average Atomic Mass

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  1. Average Atomic Mass

  2. Average Atomic Mass • atomic masses reported in periodic table represent: weighted average of masses of all naturally occurring isotopes of an element

  3. Weighted Average:Test Grades • suppose have: • 1 test of 0% and 9 tests of 90% What if I said your average was 45%? (0 + 90 = 90; divide by 2 = 45%) • would you be happy?

  4. NO! • the long way to do this problem: (90 + 90 + 90 + 90 + 90 + 90 + 90 + 90 + 90 + 0) then 10 • average = 81% • I bet you like this a lot better!

  5. The smart way to do this problem! • grades of 90: 9 out of 10 is 90% • grades of 0: 1 out of 10 is 10% 90% test grades are 90 & 10% test grades are 0 • so calc average like this… (90%)(90) + (10%)(0) = (0.90 X 90) + (0.10 X 0) = 81 + 0 average = 81%

  6. Weighted average:Smarter way to calculate average if have numerous items of differing value to average

  7. Method of Weighted Averages convert % to decimal format (divide % by 100) multiply each isotope’s abundance factor by its atomic mass find the sum

  8. Avg. Atomic Mass of Chlorine Chlorine has two isotopes Percent Abundance Mass Isotope 1 75.770% 34.969 amu Isotope 2 24.230% 36.966 amu

  9. Avg. Atomic Mass of Chlorine to estimate the answer: 75% of Cl is 34.969 amu & 25% of Cl is 36.966 amu average has to be between 34.969 amu & 36.966 amu, but closer to 34.969 amu • let’s calculate the average

  10. Avg. Atomic Mass of Chlorine = (.75770)(34.969 amu) + (.24230) (36.966 amu) = 26.496 amu + 8.957 amu = 35.453 amu sum convert % to decimals multiply by appropriate mass

  11. Avg. Atomic Mass of Si 92.21% of Si has mass of 27.97693 amu 4.70% of Si has mass of 28.97649 amu 3.09% of Si has mass of 29.97376 amu (0.9221)(27.97693) +(0.0470)(28.97649) +(0.0309)(29.97376) = 28.0856 amu

  12. sum 207.24amu Avg. Atomic Mass of Pb 1.5% Pb-204 23.6% Pb-206 22.6% Pb-207 52.3% Pb-208 (0.015)(204amu) + (0.236)(206amu) + (0.226)(207amu) + (0.523)(208amu) =

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