Periodic Law: The Origin of the Periodic Table

[sambofreemannatane]

I thought that its arranged based on atomic number?

[ChemAssistBeta]

@sambofreemannatane The original periodic table by Mendeleev was arranged in order of atomic mass. At the time, the existence and properties of subatomic particles had not yet been discovered. Since protons are so much heavier than electrons, there's no element that has more protons and is also lighter than another element (except Pa and Th, which were discovered long after Mendeleev's time). So generally, the pattern is the same for atomic mass and atomic number. Is that a good answer?