A hypothetical pure element consists entirely of two isotopes. The natural percent abun- dance of the isotope with mass 25.6 u is 47.2%. The other isotope has mass 29.7 u. Calculate the atomic weight of the naturally occurring element.
The atomic mass of an element that you see in the periodic table is the weighted average of all of the isotopes. 100-47.2 = the other isotope %.
(25.6 u x 0.472) + (0.297 u x (1.00 - 0.472) = ?