number of protons
Atomic mass was used to organize the earliest periodic table.
Mendeleev arranged the periodic table according to increasing atomic mass. This method has been used since he first developed it in the 1800s.
The periodic table organizes the elements by atomic number (number of nuclear protons).
Atomic number
Atomic Mass Octaves and Triads
it is arranged in the increasing order of atomic number.
Atomic number was not used by Mendeleev to organize his periodic table. He organized the elements based on their atomic mass and properties, leaving gaps for undiscovered elements that were later filled.
Dimitri Mendeleev
Atomic weight
The current Periodic Table is organized by each elements atomic number. The atomic number is the number of protons in the nucleus of the atom of each element.
he first organized his table in 1869 he did it by organizing them by atomic weights.
Dmitiri Mendeleev arranged the Periodic Table of elements in order of increasing atomic masses.