breaking the code
John Newlands and Dmitri Mendeleev used the idea of octaves to help them develpo the peridic table.
Orederd elements by mass maldeleevt gaps for underscoverd elements, which enabled him to maintain pattern of properties.and predicted some of the properties of the underscoverd elements. He relised iodine should come after tellurium based on chemicasl properties despite being lighter in mass.
when eke-aluminium was discovered in 1875 and matches maldevees predictions, the periodic table wad accepted.
maledeev's did not know about the atomic numbers as protns were not discovered. Fortuantly maldeleev none of the noble gases had been discovered when he suggested the periodic table if they had of been it would have been harder to come up with the table.
Noble gases, discovered between 1868 and 1898 as they were all in the same group there chemistry was simuler so they were added up as group 0 at the right handed side of the periodic table.