-
400
Democristus
A Greek philisopher Democristus was the first person to propose the idea that matter was not infinitely divisible.
Demoscristus Idea's
1.Matter is composed to empty space through which atoms move.
2.Atoms are homogeneous and cannot be divided or destroyed.
3. Different kinds of atoms have different sizes and shapes.
4. Properties of matter are based on the size, shape and movement of atoms.
5. Changes in matter result from changes in groupings of atoms. -
Period: 400 to
The Atom Theory
-
John Dalton
John Dalton, a schoolteacher revives the ideas of Democritus.
Main Points of Dalton's Theory
1.All matter is composed of extremely small partciles called atoms.
2. Atoms cannot be created, divided into smaller particles, or destroyed.
3.In a chemical reaction, atoms are seperated, combined, or reaaranged.
4. All atoms of the same element are the same shape. However, atoms of a different element are different from another element.
5. Atoms combine to form compunds. -
Amedeo Avogadro
Avogadro is known for his contribution to the molecular theory. He discovered molecules, which are an electrically neutral group of two or more atoms held together by covalent chemical bonds. -
JJ Thomson
JJ Thomson is credited for discovering electrons and isotopes.
During an experiemnt in a labratory, JJ Thomson was oberserving electricity inside empty glass tubes. This would later be called cathode ray tubes. JJ Thomson then discovers that the rays were smaller than atoms. He would later find out that rays were made of electrons. -
Robert Millikan
Millikan worked on an oil-drop experiment, which led him to discover the charge of an electron. He put a charge on a tiny drop of oil. He then measured how strong an applied electric field had to be to stop the oil drop from falling. -
Ernest Rutherford
Rutherford conducted an experiment called the gold foil experiment, which led to Rutherford discovering the nucleus of an atom. Also, he discovered the neutron and proton. He discovered that the proton had a positive charge and that a neutron had a nuetral charge.
