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330
Aristotle
330 BC-Aristole had a theory of four elements-
earth, fire, water, air. -
Antoine Lavosier
Antoine wrote the first list of elements containing 33 elements.
His elements were divided between metals and non metals but later some of the elements were found to be compounds and mixtures. -
Jons Jakob Berzelius
Jons Developed a table of atomic weights and Introduced letters to symbolize elements. -
Johann Dobereiner
Johann came up with the idea of "triads" Groups of 3 elements with similar properties.
For example-
Lithium, sodium and potassium made up a triad.
Calcium, strontium and barium is another example. -
Lothar Meyer
Lothar produced a table of 28 elements that he listed by their valence.
Valency is representing the combining power of an element.
Them 28 elements were the almost the main group of elements.
In 1868 he incorporated transition metals in another table that listed the elements in increasing weight order.
This was earlier than Dmitris table in 1869 but unfortunately for Lothar his table was published in 1870. -
Dmitri Mendeleev
Dmitri Mendeleev studied at St Petersburg and graduated in 1856.
Then in 1863 Dmitri was given a proffesorship and became the chair in the university in 1866.
Then in 1869 he arranged the 63 known elements into a periodic table and then published it in principles of chemistry. -
William Ramsay
William discovered the noble gases and in 1984 William removed oxygen, nitrogen, water and carbon dioxide from a sample of air and was left with a gas 19 times heavier than hydrogen.
1895-He discovered helium as a decay product of uranium and matched it to the emission spectrum of an unknown element in the sun that was discovered in 1868.
He went on to discover the elements neon, krypton and xenon and then realised these represented a new group in the periodic table. -
Henry Moseley
Henry determined the atomic number for each element.
Then he modified the periodic law to read that their properties vary with their atomic numbers.
1914-Then he predicted that their were 3 unknown elements between aluminium and gold and found out there were only 92 elememnts up to and including uranium.
