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300 BCE
Aristotle
Aristotle didn't believe in the atomic theory. He thought that all materials on Earth were made of the four elements; Earth, Fire, Water, and Air. -
Isaac Newton
Newton described the attractive and repulsive forces of objects having some impact on pressure. All change is caused by collisions of atoms. This showed that atoms could move and cause things to move as well. -
Antoine Lavoisier
Lavoisier is most noted for his discovery of the role oxygen plays in combustion. He also stated that when some substances were burned, their loss in mass was gas molecules escaping into the atmosphere which led him to establish the Law of Conservation of Mass. -
Solid Sphere Model - John Dalton
Developed in 1803, Dalton's theory states that all elements are composed of tiny, invisible particles called atoms. All the atoms of a given element are identical, but they differ from those of any other element. -
Plum Pudding Model - JJ Thomson
In 1897 JJ Thompson discovered the electron. His experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons. Then in 1904 proposed his atomic theory which had negatively-charged electrons embedded within a positively-charged "soup." -
Albert Einstein
In 1905 Einstein mathematically proved the existence of atoms and his atomic theory says that any liquid is made up of molecules. He is most famous for introducing the world to the equation E=mc2. -
Nuclear Model - Ernest Rutherford
In 1908 Ernest Rutherford did his famous gold foil experiment. He shot alpha particles at gold foil. His experiment showed that the atom is mostly empty space with a tiny, dense, positively-charged nucleus -
Planetrary Model - Niels Bohr
In 1913 Bohr stated that electrons in atoms move in circular orbits around a central nucleus and can only orbit stably in certain fixed circular orbits at a discrete set of distances from the nucleus. When jumping from one orbit to another with lower energy, a light quantum is emitted. -
Quantum Model - Erwin Schrodinger
In 1926 Erwin Schrödinger proposed the quantum mechanical model of the atom, which treats electrons as matter waves. Electrons have an intrinsic property called spin, and an electron can have one of two possible spin values: spin-up or spin-down.
