born 460 BC. His theory: Matter could not be divided into smaller and smaller pieces forever, eventually the smallest possible piece would be obtained.
This piece would be indivisible.
He named the smallest piece of matter “Atomos,” meaning “not to be cut.”
Born 6 September 1766. He deduced that all elements are composed of atoms. Atoms are indivisible and indestructible particles.
Atoms of the same element are exactly alike.
Atoms of different elements are different.
Compounds are formed by the joining of atoms of two or more elements.
Born 18 December 1856. He proposed a model of the atom that is sometimes called the “Plum Pudding” model.
Atoms were made from a positively charged substance with negatively charged electrons scattered about, like raisins in a pudding. Thomson studied the passage of an electric current through a gas.
As the current passed through the gas, it gave off rays of negatively charged particles.
Born 30 August 1871
Most of the positively charged “bullets” passed right through the gold atoms in the sheet of gold foil without changing course at all.
Some of the positively charged “bullets,” however, did bounce away from the gold sheet as if they had hit something solid. He knew that positive charges repel positive charges. Rutherford’s experiment Involved firing a stream of tiny positively charged particles at a thin sheet of gold foil (2000 atoms thick).
According to Bohr’s atomic model, electrons move in definite orbits around the nucleus, much like planets circle the sun. These orbits, or energy levels, are located at certain distances from the nucleus.
In 1932, James Chadwick conducted an investigation involving radiation and discovered the presence of the neutron.