The elements, if arranged according to their atomic weights, exhibit an apparent periodicity of properties.
Dmitri MendeleevThe edifice of science not only requires material, but also a plan. Without the material, the plan alone is but a castle in the air-a mere possibility; whilst the material without a plan is but useless matter.
Dmitri MendeleevI saw in a dream a table where all the elements fell into place as required. Awakening, I immediately wrote it down on a piece of paper.
Dmitri Mendeleev