If all the elements are arranged in the order of their atomic weights, a periodic repetition of properties is obtained. This is expressed by the law of periodicity.
Dmitri MendeleevElements which are similar as regards their chemical properties have atomic weights which are either of nearly the same value (eg. Pt, Ir, Os) or which increase regularly (eg. K, Ru, Cs).
Dmitri MendeleevWe must expect the discovery of many as yet unknown elements-for example, elements analogous to aluminum and silicon- whose atomic weight would be between 65 and 75.
Dmitri MendeleevWhy do they [Americans] quarrel, why do they hate Negroes, Indians, even Germans, why do they not have science and poetry commensurate with themselves, why are there so many frauds and so much nonsense? I cannot soon give a solution to these questions ... It was clear that in the United States there was a development not of the best, but of the middle and worst sides of European civilization; the notorious general voting, the tendency to politics... all the same as in Europe. A new dawn is not to be seen on this side of the ocean.
Dmitri Mendeleev