Democritus was an ancient Greek philosopher that believed all matter is consisted of extremely small particles. He called them atoms which came from the Greek word atomos which means indivisible.
0384 bc - 0322 bc
Believed all matter consisted of the five elements, water, fire, air, and earth.
Proposed a mechanical universe with small masses in motion.
1776 ad - 1844 ad
Solidified the atomic theory. He proved the existence of atoms with experiments and came to the conclusion that all elements are made of submicroscopic parts called atoms.
1791 - 1867
Studied the effect of electricity on solutions made the term electrolysis and used it to split molecules.
1826 - 1911
Proposed that electricity was made of negative particles called electrons.
James Clerk Maxwell
1831 - 1879
Proposed electromagnetic fields.
Sir William Crookes
1832 - 1919
Discovered that cathode rays have a negative charge, travel in straight lines, and cause glass to fluoresce. They caused pin wheels to spin indicating they have mass.
1834 - 1907
Created the first version of the periodic table of elements.
1845 - 1923
Using a CRT he discovered that nearby chemicals glowed. Further experimentation showed that they were penetrating rays he named X-rays.
1852 - 1908
While studding the effects of X-rays on photographic film, he discovered that some chemicals spontaneously decompose and give off penetrating rays.
1856 - 1940
Used a CRT to experimentally determine the charge to mass ratio e/m of an electron 1.759 x 10 8 coulombs/gram. Studied canal rays and found the were associated with the proton H+.
1858 - 1947
Used the idea of quanta to explain glowing hot matter.
1859 - 1860
Built one of the first cathode ray tubes.
1862 - 1962
Created the atomic model with orbital shells of electrons using the regularities of the periodic table.
1865 - 1950
Postulated a "Saturnian" model of the atom with flat rings of electrons revolving around a positively charged particle.
1867 - 1934
Studied uranium and thorium and called their decay process radio activity. Also discovered the radioactive elements polonium and radium.
1868 - 1953
Oil drop experiment determined the charge and mass of an electron.
1869 - 1910
Discovered that inert gases had a stable electron configuration which lead to their chemical inactivity. Died crashing a gas balloon.
1871 - 1937
Using alpha particles as bullets, probed the atoms in a piece of thin gold foil. He established that the nucleus was: very dense, very small and positively charged. He also assumed that the electrons were located outside the nucleus.
1871 - 1937
Studied radiation emitted from uranium and thorium and named them alpha and beta.
1877 - 1956
Observed spontaneous disintegration of radioactive elements he called isotopes or new elements.
Lise meitner, Hahn, Strassman
1878 - 1968
Discovered fission chain reaction by using heavy elements to capture neutrons and form unstable products.
1879 - 1955
E=mc2. Possibly the smartest man that has ever lived.
1882 - 1945
Developed an electrical device to click when hit with alpha particles. Created the Geiger counter.
1886 - 1887
Used a CRT to study canal rays which had electric and magnetic properties opposite of an electron.
1887 - 1915
Using x-ray tubes, determined the charges on the nuclei of most atoms. This work was used to base the periodic table off of atomic number instead of mass
1887 - 1961
Viewed electrons as clouds and introduced wave mechanics as a model of the atom.
James Chadwick (Jimmy Neutron)
1891 - 1974
Discovered a neutral atomic particle using alpha particles with a mass close to a proton, thus the neutron was born!
1892 - 1987
Discovered electrons have a dual nature, similar to both particles and waves.
1897 - 1995
Built an early linear accelerator with protons to produce alpha particles.
1901 - 1954
Controlled the first chain reaction by releasing energy from an atoms nucleus.
1901 - 1976
Described atoms by means of formula connected to the frequencies of spectral lines. Proposed Principle of Indeterminacy.
1902 - 1984
Discovered anti-particles. Discovered the anti-electron in 1932.
1912 - 1999
Synthesized 6 trans uranium elements and suggested a change in the layout of the periodic table. American scientist who won the 1951 Nobel Prize in Chemistry for discoveries in the chemistry of the trans uranium elements
1919 - 1920
Discovered the existence of isotopes using a mass spectrograph.