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400
Democritus 400BC
-Greek Philosopher
-The quest of finding the meaning of 'matter' was started by Democritus
-Matter can always be divided into smaller and smaller pieces until you reach a single unit that can no longer be divided
-That single unit Democritus called an "Atomos" meaning "Not to be cut" -
John Dalton
-Performed numerous experiments that led to the break through of accepting atoms.
-THEORY:
-Atoms are indivisible and indestructable particles
-Atoms of a given element are exactly the same in structure and properties but those of different elements are different.
-Atoms of different elements form to create compounds. -
Dmitri Medeleez
-one of the first pioneers of the atomic theory
-He drew up a table allocating various elements into 7 groups of similar properties.
-Arranged according to weight and with each elemet they were given a symbol. This is now known as the Periodic Table. -
J.J Thomson
-Discovered that atoms were made from a positively charged subsatnce with negatively charged electrons scattered haphazardly. -Thomson conducted various experiments and concluded that there had to be particles that were smaller than the atom however the charge was neutral, from this he found that there must be both positive and negative charges within the atom but unfortunatley he was never able to find the positive charges -
Earnest Rutherford
-Rutherford conducted an experiment envolving a thin sheet of gold, he then fired a stream of positively charged particles at the sheet
-He found that most of the positive charges went through but some rebounded, Rutherford knew that a positive and a positive repelled eachother.
-He concluded that an atom had a positive charged center which he then called, what is known today as a 'Nucleus'. -
Niels Bohr
-In Bohr's model he organised each electron into a specific energy level, he prosposed that electrons move in definite orbits (like the planets circle the sun)