We all know what isotopes are , they may be the same element and also have the same atomic number but will have different atomic mass , they are called isotopes , for example Carbon - 12 , Carbon 13 and carbon - 14 , they are some examples of isotopes.
Isobars are atoms which have the same number mass number of atoms from a other element , for example we have calcium which have 20 protons and 20 neutrons while we also have atoms which have 18 protons and 22 neutrons and that is Argon-40
Atomic Mass And Relative mass
How do we measure mass at such a small scale? Well to do that the chemistry community has historically used something called an atomic mass unit. I'll write it here, atomic, atomic mass unit, and it's historically denoted as AMU. And more recently, the more modern version of these are the unified atomic mass unit, that is denoted by just a U instead of an AMU.
Well, the unified atomic mass unit is defined as1.660540 times 10^-27
Relative atomic mass is a avg mass of a element
Example of relative mass : We have hydrogen , if we add all the mass of the hydrogen isotopes and hydrogen itself and divide it by the isotopes amount number and hydrogen we would get a avg value of 1.00784