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.

Believed all matter consisted of the five elements, water, fire, air, and earth.

Proposed a mechanical universe with small masses in motion.

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.

Studied the effect of electricity on solutions made the term electrolysis and used it to split molecules.

Proposed that electricity was made of negative particles called electrons.

Proposed electromagnetic fields.

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.

Created the first version of the periodic table of elements.

Using a CRT he discovered that nearby chemicals glowed. Further experimentation showed that they were penetrating rays he named X-rays.

While studding the effects of X-rays on photographic film, he discovered that some chemicals spontaneously decompose and give off penetrating rays.

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+.

Used the idea of quanta to explain glowing hot matter.

Built one of the first cathode ray tubes.

Created the atomic model with orbital shells of electrons using the regularities of the periodic table.

Postulated a "Saturnian" model of the atom with flat rings of electrons revolving around a positively charged particle.

Studied uranium and thorium and called their decay process radio activity. Also discovered the radioactive elements polonium and radium.

Oil drop experiment determined the charge and mass of an electron.

Discovered that inert gases had a stable electron configuration which lead to their chemical inactivity. Died crashing a gas balloon.

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.

Studied radiation emitted from uranium and thorium and named them alpha and beta.

Observed spontaneous disintegration of radioactive elements he called isotopes or new elements.

Discovered fission chain reaction by using heavy elements to capture neutrons and form unstable products.

E=mc2. Possibly the smartest man that has ever lived.

Developed an electrical device to click when hit with alpha particles. Created the Geiger counter.

Used a CRT to study canal rays which had electric and magnetic properties opposite of an electron.

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

Viewed electrons as clouds and introduced wave mechanics as a model of the atom.

Discovered a neutral atomic particle using alpha particles with a mass close to a proton, thus the neutron was born!

Discovered electrons have a dual nature, similar to both particles and waves.

Built an early linear accelerator with protons to produce alpha particles.

Controlled the first chain reaction by releasing energy from an atoms nucleus.

Described atoms by means of formula connected to the frequencies of spectral lines. Proposed Principle of Indeterminacy.

Discovered anti-particles. Discovered the anti-electron in 1932.

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

Discovered the existence of isotopes using a mass spectrograph.