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404
BC Greek Era Democritus
Theorized that all matter is made of atoms which became known as the atomic theory. Came up with the idea that atoms are in a void. -
Period: 404 to
Atomic Theory Timeline
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Sir Isaac Newton
Began experimenting to understand how matter was structured and in 1704 proposed that the universe is made up of small particles of mass in motion. -
John Dalton
Experimented the atomic theory on solid conclusions not on pure chance. Came up with a model which concluded that atoms are solid, combined in ratios to form compounds (law of conservation and mass and law of constant composition). 1803 published his atomic theory. -
Dmitri Mendeleev
Arranged similar properties of elements in several groups which were atomic weights of periodic functions. His arrangement became known as the Periodic Law. -
James Clerk Maxwell
Came up with the proposal of electric and magnetic fields filling the atomic void. Experimented with electricity and achieved the electromagnetic theory. Demonstrated electricity and magnetism flowing in waves at the speed of light. -
J.J. Thompson
Studied electric currents by using a glowing beam to apply voltage to two metal plates. He then placed a magnet to a tube and the negatives repelled while the positives pulled. Thus he discovered the Cathode Ray Tube was negatively charged. Discovered electrons. Came up with the Plum Pudding model -
Ernest Rutherford
First in 1898 studied energy radiations naming them alpha and beta particles. Now in 1911, Rutherford experimented with the alpha particles by shooting them at gold foil. Some passed, some shot through, concluding that the center of an atom is positive (protons) and an atom contains empty space. This empty space is known as the nucleus and holds most of the mass of the atom. Made the assumption that electrons orbit the nucleus like planets -
Frederick Soddy
Worked with Ernest Rutherford on the study of radiation. Did much chemical work and came up with the concept of isotopes stating certain elements can exist in two or more states with the same atomic number but different amount of neutrons . -
Henry Moseley
Worked with X-ray tubes and found that all elements have a certain atomic number. "Atomic number in the nucleus is equal to number of protons" Published his results which reorganized the Periodic Table to be based on atomic number instead of atomic mass. -
Niels Bohr
Experimented with "shell spectra" with the spectra scope. Came up with the Bohr's Model which states that electrons orbit the nucleus in shells, and can be bumped up to higher shells by an electron or photon of light (photons produce when electrons fall down). Described his electron work in energy levels. -
James Chadwick
Used alpha particles to prove a neutral atomic particle- the neutron. Discovered neutron has no charge but rather an attractive force which stabilizes the nucleus .
