How to find atomic mass of an elemen t I know you will say

Last updated: 7/4/2023

How to find atomic mass of an elemen t I know you will say Number of proton s Number of neutrons for example ox ygen atomic 16 8 8 Number of pro tons Number of neutrons but how the chlorine have mass of 35 5 amu I know also this very well Because of the average mass of their isotopes b ut I want to know that oxygen also have isotopes but its atomic mass Number of protons Number of neutro ns why in the case of oxygen we don t c alculate the average of the mass of thei risotopes