Why did early scientists use atomic mass?

Newlands' octaves. An English scientist called John Newlands put forward his Law of Octaves in 1864. He arranged all the elements known at the time into a table in order of relative atomic mass. When he did this, he found a pattern among the early elements. read more

Atomic mass could be measured and was a known quantity. Atomic number is based on the number of protons. The number of protons could not yet be measured. Early scientists could only used atomic mass. read more

Mendeleev also arranged the elements known at the time in order of relative atomic mass relative atomic mass: The relative atomic mass is the number of times heavier an atom is compared to one twelth of a carbon-12 atom., but he did some other things that made his table much more successful. read more