Anewly 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?

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 :

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