I already showed you the atomic mass.
That is why this says atomic number, but for most intents and purposes we can say this could be atomic mass.
Mendeleev is the one who taught us that the properties of the elements are a function of the atomic mass.
"Alpha particles have two positive charges and a mass of four atomic mass units; they are identical to helium nuclei. Though they are emitted at speeds about one-tenth that of light, they are not very penetrating and have ranges in air of about 1-4 in. (2.5-10 cm)."
They have the same atomic number and hence nearly identical chemical behaviour but different atomic masses.
The same man. Other classifications, Dobereiner People, remember, they were measuring atomic masses.
