Events
Democritus
400BCE- He made the theory saying that matter is made of small particles that are
invisible and indestructible and was called the atomic theory.
Atoms of every element have always been and always will be in motion, a
nd there is an infinite number of atoms that differ in size and shape.Aristotle
3000BCE- He believed that everything on
Earth was made of 4 elements; Earth, Water,
Fire and AirRobert Boyle
1662- He discovered that elements were not only earth, air, water
and fire. He found that those things could decompose into simpler
substances, and the most simplest were the elements.
He also discovered Boyle’s Law.Antoine Lavoisier
1789- He wrote the first extensive list of the 33 known elementsJohn Dalton
1808- He created the Dalton Theory. He thought that the atoms of different
elements looked different but the ones of the same were the same.
He also gave an atomic weight to each of the 20 elements he knew of and
gave them symbols so it was easier to draw them.Jons Jacob Berzelius
1828- compiled a table of relative atomic weights.
He invented the modern system of chemical notation and established
the basic symbols for the elements as used todayJohann Dobereiner
1829- Noticed that Bl, Cl and I had similar properties
and that Bl’s atomic mass was between the other 2. He found 3
other groups with similarities. He called them triads.John Newlands
1864- Arranged the known 62 elements from lightest to heaviest.
He noticed that every 8th element had similar chemical and physical properties.
Became known as Newland’s law of octavesAlexandre Beguyer de Chancourtois
1862- was the first to arrange the chemical elements in order of atomic weightsDmitri Mendeleev
1869- organised the elements by atomic mass but made it into a table form.
Elements with similar properties were put into the same column.
Left blanks where he believed missing elements were, and he was
correct. Gave rise to the Periodic Law which was properties
of elements are periodic functions of their atomic mass.Lothar Meyer
1864- Published his own version of the periodic table.
Plotted a graph of atomic volume vs atomic weightMarie and Pierre Curie
1898- they discovered an element 400 times more radioactive
than uranium. Called it poloniumWilliam Ramsay
1895- Discovered the noble gases. He predicted the existence of them.Henry Mosely
1913- arranged the elements by atomic number.
This gave rise to the new periodic law: Properties of elements are
periodic functions of their atomic number.Periods
Glen Seaborg
1912 to 1999- Discovered 8 new elements. The only living person for whom an element was named.
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