Question

Why is atomic number considered to be more appropriate than atomic mass for classification of elements

Answer 1

this is because if you see the mendeleev's periodic table you will notice that the position of ce and ni is inappropriate ce has atomic mass 58.93 and ni has 58.71 so ni should be placed before ce. but if you see the modern periodic table which is based on atomic number has no such errors

Answer 2

According to the modern periodic law: the properties of elements are a periodic function of their atomic numbers .Actually when elements are arranged according to increasing atomic numbers,there is a periodicity in the electronic configuration of elements leads to the periodicity in their chemical properties. The real significance of the modern periodic classification based on their atomic numbers is that it relates the periodicity in their electronic configurations.