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A newly discovered element, Y, has two naturally occurring isotopes. 87.8 percent of the sample is an isotope with a mass of 267.8 u, and 12.2 percent of the sample is an isotope with a mass of 269.9 u. What is the weighted average atomic mass for this element?

User Shamsup
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2 Answers

4 votes
(0.878)(267.8) + (0.122)(269.9)=

268 u (three sig fig)


Check my calculations
User Collin Peters
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4 votes

Answer : The average atomic mass of an element is, 268.6 amu.

Solution : Given,

Mass of isotope 1 = 267.8 amu

% abundance of isotope 1 = 87.8% = 0.878

Mass of isotope 2 = 269.9 amu

% abundance of isotope 2 = 12.2% = 0.122

Formula used for average atomic mass of an element :


\text{ Average atomic mass of an element}=\sum(\text{atomic mass of an isotopes}* {{\text { fractional abundance}})


\text{ Average atomic mass of an element} Y=\sum[(267.8* 0.878)+(269.9* 0.122)


\text{ Average atomic mass of an element}=268.06amu

Therefore, the average atomic mass of an element is, 268.6 amu.

User TamusJRoyce
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8.6k points
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