The periodic table summarizes an entire science in 100 or so squares containing symbols and numbers.

The periodic table enumerates the elements that compose all earthly substances, arranged so as to reveal patterns in their properties, guiding the pursuit of chemical research both in theory and in practice.

The periodic table is not the most important concept in chemistry.

The periodic table symbolizes not merely the constituents of matter, but the logical cogency and principled rationality of all science.

German chemist Johann Wolfgang Döbereiner noticed peculiarities in groupings of elements as early as 1817.

The New System of Chemical Philosophy was written by

Dalton was never wrong about the atom weights

Who noticed that arranging the known elements in order of increasing atomic weight produced a recurrence of chemical properties every eighth element, a pattern he called the “law of octaves”

Who discovered the atomic nucleus

By the time of Mendeleev’s death in 1907, scientists knew that atoms had parts: electrons, which carried a negative electric charge, plus some positively charged component to make atoms electrically neutral.

The Danish physicist (name) realized that quantum theory governed the arrangement of electrons surrounding the nucleus and that the outermost electrons determined an element’s chemical properties.