jan 3, 1869 - Dimitri Mendellev used John Newlands'
grouping and organized the elements into what
is now known as the periodic table. He used the
atomic mass as the primary characteristic to
decide where each element belonged in his
table. The elements were arranged in rows and
columns. He even left spaces for elements to be
discovered because of the pattern he saw once
he started organizing those elements known at
that that time.
Added to timeline:
History of the Periodic Table