How do you find the average atomic mass?

1 Answer
Slangus
Nov 11, 2015

When calculating the average atomic mass of an element you should be given the isotope and the percent abundance. For example (X is a made up element).

#X-45# = 44.8776 amu is 32.88% abundant.
#X-47# = 49.9443 amu is 67.12% abundant.

Note: amu stands for atomic mass unit

Given that information, you multiply the amu by the percent abundance

#.3288(44.8776) = 14.75575#
#.6712(46.9443) = 33.52261#

Then you add the two figures together to get your average atomic mass.

#14.75575+33.52261 = 48.27836#

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