-
In 400 BC Democritus created a model of a round spherical atom with no protons, neutrons, or electrons.
-
-
His atomic theory was: All matter is made of invisible and indestructible atoms. Atoms of any given element are identical in mass and properties. Compounds are formed by 2 or more different types of atoms. A chemical reaction is the rearrangement of atoms.
-
In 1904 Thomson suggested a new model of a sphere with a positive charge and negative electrons positioned outside of it.
-
In 1907 he also discovered elements atomic number. He discovered the atomic nucleus.
-
His theory was that an atom contains positive nucleus and negatively charged electrons orbiting the nucleus.
-
In 1913, Millikan dicovered that atoms have a negative charge in them.
-
In 1932 Chadwick discovered the neutron, a neutron has a neutral charge, and that it is found in the nucleus of an atom.
