Why was the basis is classificatons of elements changed from the atomic mass to the atomic number ?

Define atomic mass number.

Why do elements have different atomicities?

Who classified elements according the their atomic numbers ?

Atomic mass of the element Sulphur-

An element M has an atomic mass 19 and atomic number 9. Its ion is represented by

What are inner transition elements? Decide which of the following atomic numbers are the atomic numbers of the inner transition elements : 29, 59, 74, 95, 102, 104.

Why is an atom of one element different from the atoms of other elements?

Atoms of different elements having same mass number but different atomic numbers are called

What is atomic mass of an element?