<<1800-1875>>



-John Dalton- ( 1776 - 1844) Origin; England

John Dalton views atomism by way of meteorology. He would keep daily weather records from 1787 until his death. Dalton clarified that air is not a cast chemical solvent but a mechanical system. Said the pressure exerted by a gas in a mixture is independent of the pressure exerted by other gases. Dalton would claim atoms in a mixture were different in weight and complexity. Calculated atomic weights from percentage compositions using an arbitrary system. This would determine the atomic structure of each compound. Dalton said if there are two elements that combine, then their combination will occur in a set sequence. Wrote his theories in his book //New System of Chemical Philosophy.// .

-Sir William Crookes- (1832-1919) Origin: London, England Discovered: Thallium (1861)

Sir William Crookes discovered Thallium in 1861 after conduction spectroscopic exams of the residue left in manufactured sulfuric acid. He noticed a bright green line which he later discovered to be Thallium. For Eight years Crookes would conduct investigations of this new metal and its properties. When he was determining the atomic weight, Crookes thought for accuracy he should measure this new metal in a vacuum. He found the metal to heavier when cold than when it was hot. Crookes explained this to be a "repulsion from radiation." Crookes later constructed the radiometer which transformed light into motion. He would develop a theory of "radiant matter" from the discharge of electricity through exhausted tubes, also known as "Crookes Tubes."





-Dmitri Mendeleev- (1834-1907) Origin: Russia Worked on Periodic Table

Dmitri Mendeleev is most famous for his work that he did on the Periodic Table. Mendeleev did cover work from applied Chemistry to most problems of Chemical and Physical theory. He gave full expressions to generalization of elements that others traced, and he even questioned the correctness of "accepted atomic weights" because they did not correspond to the Periodic Table. Due to certain gaps in his tables in 1871, Dmitri was led to the existence of three new elements; ekaboron, ekaaluminium, and ekasilicon. In 1902, Mendeleev put together the hypothesis that two elements exist with a smaller atomic weight than hydrogen; "aether." For his work on the Periodic table, Dmitri Mendeleev recieved the Davy Award of Royal Society in 1882 and the Copley Medal in 1905.