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440 BCE
Democritus
Democritus was a Greek philosopher who made one of the greatest contribution to modern science. He made an atomic theory with his mentor Leucippus about the universe and all matter. These following principles include:
1.All matter consists of invisible particles called atoms.
2. Atoms are indestructible.
3. Atoms are solid but invisible.
4. Atoms are homogenous.
5. Atoms differ in size, shape, mass, position, and arrangement. -
John Dalton
John Dalton was an English chemist, physicist, and meteorologist. He created 'Dalton's law', a law proposed that the amount of pressure exerted by a mixture of gases in a fixed volume is equivalent to all of the pressures that would be exerted by each gas alone in the same volume. -
Mendeleev
Mendeleev was a Russian chemist and inventor. He formulated the Periodic Law. He and Lothar Meyer came up with their own periodic table "when the elements are arranged in order of increasing atomic mass, certain sets of properties recur periodically.". -
William Ramsay
William Ramsay was a British chemist who discovered noble gases and received a Nobel Prize in Chemistry in 1904 "in recognition of his services in the discovery of the inert gaseous elements in air". He discovered four gases (neon, argon, krypton, xenon) and proved that helium and radon make a whole family of elements, noble gases. -
JJ Thomson
JJ Thomson was an English physicist and Nobel Laureate in Physics. He discovered electrons and that atoms could be divided. He also proposed atoms are made of positive cores and negatively charged particles within it. -
Ernest Rutherford
Ernest Rutherford was a Zealand-born British physicist who created the 'Rutherford model'. The Rutherford model is a gold foil experiment where he demonstrated that the atom has a tiny and heavy nucleus. He designed the experiment to show the alpha particles emitted by a radioactive element as probes to the unseen world of atomic structure. -
Neils Bohr
Neils Bohr was a Danish physicist who made foundational contributions to understanding atomic structure and quantum theory. He created the 'Bohr theory', in which the hydrogen atom is stated to have one proton in the nucleus with an electron orbiting around it, each orbit corresponding to a specific quantized energy state. -
Henry Moseley
Henry Moseley was an English physicist who made a contribution to the previous Periodic Law discovered by Mendeleev. Moseley justified the concept of the empirical and chemical arrangement of the atomic number. He proved this by stating that Iodine has a higher atomic number than Tellurium.
