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WEIGHTED AVERAGE MASS NUMBER: 1)The mass number on the periodic table is calculated from the weighted average of the most abundant isotopes. 2) Abundance.

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Presentation on theme: "WEIGHTED AVERAGE MASS NUMBER: 1)The mass number on the periodic table is calculated from the weighted average of the most abundant isotopes. 2) Abundance."— Presentation transcript:

1 WEIGHTED AVERAGE MASS NUMBER: 1)The mass number on the periodic table is calculated from the weighted average of the most abundant isotopes. 2) Abundance is presented as a percentage, however it is expressed as a decimal in any calculations. 3) The most abundant isotope will have a mass number closest to the weighted mass number average. EXAMPLE FOR ELEMENT X, 30%(0.30) OF THE ATOMS ARE X-40, 20%(0.20) ARE X-45 AND 50%(0.50) ARE X-47. NOTE X-40 IS USUSALLY REPRESENTED AS 40 X. INTERPRETATION: 30 OUT OF 100 ATOMS ARE X-40 20 OUT OF 100 ATOMS ARE X-45 50 OUT OF 100 ATOMS ARE X-47

2 SKILL #2)--- WEIGHTED AVERAGE MASS NUMBER CALCULATION. 1)PERCENTAGE ABUNDANCES TO DECIMALS CONVERT ALL THE. 2)MULTIPLY THE DECIMAL ABUNDANCE BY THE MASS NUMBER OF THAT ISOTOPE TO GET THE WEIGHTED SUBTOTAL. 3)ADD THE WEIGHTED SUBTOTALS TO GET THE WEIGHTED AVERAGE MASS NUMBER. EXAMPLE)--- WEIGHTED AVERAGE MASS NUMBER CALCULATION. CALCULATE THE MASS NUMBER OF ELEMENT X WHERE,: 30%(0.30) OF THE ATOMS ARE X-40, 20%(0.20) ARE X-45 AND 50%(0.50) ARE X-47 1)CONVERT ALL THE PERCENTAGE ABUNDANCES TO DECIMALS. 20%/100 = 0.20 30%/100=0.30 50%/100=0.50.

3 EXAMPLE)--- WEIGHTED AVERAGE MASS NUMBER CALCULATION. CALCULATE THE MASS NUMBER OF ELEMENT X WHERE,: 30%(0.30) OF THE ATOMS ARE X-40, 20%(0.20) ARE X-45 AND 50%(0.50) ARE X-47 1)CONVERT ALL THE PERCENTAGE ABUNDANCES TO DECIMALS. 20%/100 = 0.20 30%/100=0.30 50%/100=0.50 2) MULTIPLY THE DECIMAL ABUNDANCE BY THE MASS NUMBER OF THAT ISOTOPE TO GET THE WEIGHTED SUBTOTAL ISOTOPE MASS # OF ISOTOPE (amu) FRACTIONAL ABUNDANCE SUBTOTAL MASS(amu) X-4040 x0.30 =12.0 X-4545 x0.20 = 9.0 X-4747 x0.50 =23.5

4 ISOTOPE MASS # OF ISOTOPE (amu) FRACTIONAL ABUNDANCE SUBTOTAL MASS(amu) X-40 ( 40 X)40 x0.30 =12.0 X-45 ( 45 X)45 x0.20 = 9.0 X-47 ( 47 X)47 x0.50 =23.5 + 44.50 AMU ADD THESE TO GET THE MASS AVERAGE WEIGHTED AVERAGE AS ON PERIDIC TABLE

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