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Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,*,Average Atomic Mass,What is average atomic mass?,Average atomic mass is the,weighted average,of the atomic masses of the naturally occurring isotopes of an element,Calculating a Weighted Average,Example,A box contains two size of marbles.If,25.0%have masses of 2.00 g and 75.0%,have masses of 3.00 g what is the weighted,average?,(.250)(2.00)+(.750)(3.00)=.500+2.25=,2.75g,Calculating Average Atomic Mass,EXAMPLE,Boron has two isotopes:,B-10(mass 10.013 amu)19.8%abundance,B-11(mass 11.009 amu)80.2%abundance,Calculate the average atomic mass.,(.198)(10.013)+(.802)(11.009)=,1.98 amu +8.83 amu =,10.81 amu,Calculating Average Atomic Mass,Calculate the average atomic mass of Mg.,Isotope 1-23.985 amu(78.99%),Isotope 2-24.986 amu(10.00%),Isotope 3 25.982 amu(11.01%),(23.985)(.7899)+(24.986)(.1000)+(25.982)(.1101),18.95 amu+2.499 amu+2.861 amu=,24.31 amu,Average Atomic Mass,Helium has two naturally occurring isotopes,He-3 and He-4.The atomic mass of helium is 4.003 amu.Which isotope is more abundant in nature?,He-4 is more abundant in nature because the atomic mass is closer to the mass of He-4 than to the mass of He-3.,Isotopic Pennies number of pre and post 1982,a.Let X be the number of pre-1982 pennies,b.Let 10-X be the number of post-1982 pennies,c.(X)(3.1g)+(10-X)(2.5g)=mass of 10 pennies,pre-82 post-82,EXAMPLE(Mass of a sample of pennies is 31.0g),(X)(3.1g)+(10-X)(2.5g)=31.0 g,3.1X+25-2.5X=31.0g,.6X+25=31.0g,.6X=6.0g X=6.0g/.6,X=,10 pre-82 pennies,10-X=,0 pre-82 pennies,Isotopic Penny Lab-Average Atomic Mass,Calculate percent of pre-82 and post-82 pennies,#of pre-82 pennies,x 100%,#post-82 pennies,x 100%,10 10,Calculate the average atomic mass of coinium,(%pre-82)(3.1g)+(%post-82)(2.5)=,average atomic mass,
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