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1543
SUN AT CENTER
Astronomy fans commemorate 1543, when Copernicus placed the sun at the center of the solar system. -
DALTON NEW SYSTEM
In his New System of Chemical Philosophy, Dalton explained chemical reactions by assuming that each elementary substance was made of a particular type of atom. -
GROUPING OF ELEMENTS
German chemist Johann Wolfgang Döbereiner noticed peculiarities in groupings of elements as early as 1817. -
Period: to
DIMITRI MENDELEEV
Mendeleev since he was born in Tobolsk, SIberia Dimitri had a life with a lot of studies in science and writing a lot of important investigations and science texts. -
MENDELEEV'S PERIODIC TABLE
Mendeleev’s periodic table, published in 1869, was a vertical chart that organized 63 known elements by atomic weight. This arrangement placed elements with similar properties into horizontal rows. -
MENDELEEV MADE ENOUGH ADVANCES
By early 1869, Mendeleev had made enough progress to realize that some groups of similar elements showed a regular increase in atomic weights; other elements with roughly equal atomic weights shared common properties. It appeared that ordering the elements by their atomic weight was the key to categorizing them. -
GALLIUM MADE NEW DISCOVERED
Gallium, for instance, discovered in 1875, had an atomic weight (as measured then) of 69.9 and a density six times that of water. -
IMPORTANT DECLARATION
German chemist Johannes Wislicenus declared that the periodicity of the elements’ properties when arranged by weight indicated that atoms are composed of regular arrangements of smaller particles. -
FLATTERY TO MENDELEEV
In 1900, the future Nobel chemistry laureate William Ramsay called it “the greatest generalization which has as yet been made in chemistry. -
ERNEST RUTHERFORD AND HIS IMPORTANT DISCOVERED
A key clue to how those parts were arranged came in 1911, when the physicist Ernest Rutherford, working at the University of Manchester in England, discovered the atomic nucleus. -
BOHR AND HIS OWN VERSION
Bohr created his own version of the table in 1922, based on experimental measurements of electron energies (along with some guidance from the periodic law). -
ELEMENT 101
Element 101, discovered by Seaborg and colleagues in 1955 and named mendelevium — for the chemist who above all others deserved a place at the periodic table.
