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460 BCE
Democritus
In Democritus’s model there were no proton, neutron or electron. The theory of Democritus held that everything is composed of "atoms". Of the mass of atoms, Democritus said, "The more any indivisible exceeds, the heavier it is". But his exact position on atomic weight is disputed. In Democritus view atoms :
I. Were Solid.
II. They were different In size, shape, mass, position and arrangement.
III. Invisible.
The atomic theory told that: the universe is composed of 2 elements. -
460 BCE
Aristotle
Aristotle did not believe in the atomic theory and he taught so otherwise. He thought that all materials on Earth were not made of atoms, but of the four elements, Earth, Fire, Water, and Air. He believed all substances were made of small amounts of these four elements of matter. -
John Dalton
His major contribution was his theory on atoms which consisted of 5 parts stating that matter is composed of super small particles called atoms, atoms are indivisible and indestructable, atoms of a given element are identical in size, mass, and chemical properties,atoms of specific elements are different than those of other elements, and in a chemical reaction, atoms separate,
combine and/or rearange. He made alot of observations based off his results. -
Robert Brown
Particles in both liquids and gases (collectively called fluids) move randomly. This is called Brownian motion. They do this because they are bombarded by the other moving particles in the fluid. Larger particles can be moved by light, fast-moving molecules. Brownian motion is named after the botanist Robert Brown, who first observed this in 1827. He used a microscope to look at pollen grains moving randomly in water. At this point, he could not explain why this occurred. -
Albert Einstein
invented a new method of counting and determining the size of the atoms or molecules in a given space and in the other he explains the phenomenon of Brownian motion. The net result was a proof that atoms actually exist
