How is atomic mass computed?

Answer 1

The atomic weight of an element is the average of the Atomic Mass of each individual isotope of that element, weighted by the natural abundance of each isotope.

In other words, as an example, if we had an element called "X" that had two isotopes, with mass 10 and 20, and each isotope had the same abundance, then the atomic weight of X would be 15 (that is (10+20)/2 = 15). But if the same element X had the same two isotopes, but now the abundance of the lighter isotope was 90% and the abundance of the heavier isotope was only 10%, then the atomic weight would be much less due to the difference in abundance; that is you would not take a weighted average: 0.9*10 + 0.1*20 = 11.

See the Web Link to the left for a chart of all the isotopes of the elements, their individual masses, and their natural abundances. It is with such a chart that the actual atomic weights are calculated.

Answer 2

based on the isotopes and the percentage of existence in the universe, all the masses get calculated and the atomic mass is calculated. it is good to watch out that atomic mass number is different than the atomic number.

Answer 3

Atomic mass is computed by taking into account the mass of each isotope of the element and its relative abundance in nature. The atomic mass listed on the Periodic Table is a weighted average of the masses of all the naturally occurring isotopes based on their abundance. This value is expressed in atomic mass units (amu).