Why is the atomic number of an element more important than its atomic mass in the context of its properties ?

Explanation

Chemical properites of elements depend on the number of electons present in an atom and their arrangement in different orbits .The number of electorns in an atom is equal ot that of protons and the number of protons is known as atomic number which is unique for each element .Hence atomic number is a more fundamental property than atomic weight .Atomic weights of two elemetns can be almost same .For example atomic weights of calcium and argon are 10.1 and 39.9 respectively .But there is no similarity between these two elements