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430 BCE
Democritus
Abdera, Greece. Proposed the first idea that all things in universe were made up of tiny indestructible or invisible particles called "atomos". His discovery was questioned many times because his lack of evidence with the chemical side of his idea. since the, oxidation and reaction rate have been discovered. -
John Dalton
Eaglesfield, England. Proposed that matter is made up of atoms that are indivisible and indestructible, all atoms are identical, atoms of different elements have different chemical properties, atoms of different elements combine in simple whole numbers to form compounds, and atoms cannot be created or destroyed. -
J.J. Thomson
Cheetham Hill, England. Thomson used cathode rays to determine the charge to mass ratio of the electron. He proposed that all matter is made up of tiny particles that are smaller than atoms. He called them"corpuscles" but are now known as electrons. -
Ernest Rutherford
Brightwater, New Zealand. Proposed that an atom had a central positive nucleus with negative electrons orbiting around it. He developed this their with his famous, gold foil experiment. -
Niels Bohr
Copenhagen, Denmark. Bohr came up with the quantum theory that states energy can be transferred in set quantities. Also suggested that electrons can move and be transferred, but only in certain orbits. Since his discovery, his model has been improved by physicist, Arnold Sommerfeld. This recent model of subatomic particles suggest that the orbit of electrons and elliptical and not circular. -
Robert Millikan
Missouri,Ill.(U.S.A).Determined the unit charge of the electron with his oil drop experiment. Which created the calculation of the of an electron and the positively charged atoms. -
Louis de Brogile
Dieppe, France. Brogile believed that electrons could act as particles and waves, just like light did. He proposed that certain energy, frequency and wavelengths can be determined by certain waves produced by electrons. He dicovered that electrons can act as waves which gave explanation to a lot of unexplained theories. -
Erwin Schrödinger
Austria, Ireland. Schrödinger took the Bohr atom model one step further. Schrödinger used mathematical equations to describe the likelihood of finding an electron in a certain position. This atomic model is known as the Quantum Mechanical model of the atom. This model can be portrayed as a nucleus surrounded by an electron cloud. Where the cloud is most dense, the electron is less likely to be in a less dense area of the cloud. This model introduced the concept of sub-energy levels. -
James Chadwick
Bollington United Kingdom. Chadwick attacked beryllium atoms with alpha particles. An unknown radiation was produced , in result. He proposed that the type of radiation was made up of particles that contained a neutral charge and had an equal mass to the proton particle . In conclusion, the neutron was discovered. this opened up an accurate model of an atom to chemists.
