Calculating Average Atomic Mass. Unit 9 worksheet 2. Average atomic mass. The decimal number on the periodic table The weighted average of all the isotopes of an element Depends on the percent (relative) abundance and the mass of each isotope Measured in “atomic mass units” (amu). Problem 1.
Unit 9 worksheet 2
Average atomic mass = [(mass) x (abundance)] + [(mass) x (abundance)]
[(6) X (0.075)] + [(7) x (0.925)]
0.45 + 6.475
On the periodic table, this is closest to Li, atomic number 3.