A concept that looks too hard is easily simplified here :
How do we measure the mass of the subatomic particles , or masses of atoms
We can not compare them to the Kg or even the gram since they are very very tiny , otherwise the mass will show us a very small funny number
so we have to compare their masses to a smaller fixed unit which is reasonably small that their masses can compare to
we will take the carbon atom as our reference unit , and we will say that the carbon atom has 12 units . so each unit or *relative atomic mass unit = 1/12 of mass of carbon atom
Anything that we measure after that should follow this unit
like
A proton has a mass unit of 1 , that is 1/12 of the mass of Our reference carbon atom
A Neutron also has the the same mass unit of 1 = 1/12 of the carbon atom
The carbon atom that we use has to be of a special type , it should be from the type that contains 6 protons and 6 neutrons , so its total mass is 12 units , we call this the carbon 12 atom
Are there any other carbon atoms ,
yes the carbon 14 is an isotope of carbon 12. It has 6 protons but different number of neutrons (6) . we don't use this isotope as reference , we use only carbon 12 atom as our reference .
