How can you find average atomic mass please tell me with brief explanation?

Answer 1

Average Atomic Mass refers to the weighted average of the masses of all the isotopes of an element---weighted by their abundance on earth. To find the average atomic mass you multiply the atomic mass of each isotope by its % abundance, add them all up, and divide by 100%. For instance, say that and element had three isotopes---X, Y, and Z: X has a mass of 10 and makes up 25% of all atoms of that element found on earth. Y has a mass of 11 and makes up 40% of all atoms of that element found on earth. Z has a mass of 13 and makes up 35% of all atoms of that element found on earth. The average atomic mass would be: average atomic mass = (10*25%+ 11*40% + 13*35%)/100% = 11.45 Note: I realize my answer had too many sig figs but I wanted to keep the numbers simple while still illustrating the point that the number comes out weighted more towards the heavier isotopes.