how do we caculate average atomic mass?

Asked by Balaji J | 20th Dec, 2013, 06:36: PM

Expert Answer:

Average atomic mass is the weighted average of the atomic masses of the naturally occurring isotopes of an element.


To find the average atomic mass of an atom, we take into account all of the isotopes that exist and the percentage of each type.


Average atomic mass = (Mass of isotope × Relative abundance)



To calculate average atomic mass of copper, we write the information about copper’s isotopes into the formula and solve it.


Average atomic mass of copper = (62.93 amu × 0.6909) + (64.94 amu × 0.3091) = 63.55


From the calculation, we can get an average atomic mass of copper i.e, 63.55 amu.


You can calculate the atomic mass (average) of chlorine using the following data:


% Natural Abundance

Molar Mass







The average atomic mass of chlorine




= 26.4959 + 8.9568


= 35.4527 u

Answered by Hanisha Vyas | 20th Dec, 2013, 07:14: PM

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