-
340
Aristotle
There are 5 elements in matter: air, earth, water, fire, and Aether. -
460
Democritus
Democritus adopted the atomic theory. The atomic theory asserted that the universe is composed of two elements, the atoms and the void in which they exist and move. -
Antoine Lavoisier
Determined the Law of Conservation of Matter by extensive experimentation. -
Joseph Louis Proust
Detemined the law of constant composition. -
John Dalton
formulated an atomic theory of matter with 4 postulates, whcin were: 1. Elements are composted of small particles called atoms.
2. All atoms of a given element are identical. 3. Atoms are neither created nor destroyed in chemical reactions. 4. Compounds always contain the same proportion of elements. -
Henri Becquerel
Henri Becquerel discovered some chemicals spontaneousely decompose and give off pentrating rays while studying the effect of x-rays on photographic film. -
J.J. Thomson
J.J. Thomson performed a CRT experiment and determined that the ray was composed of negative particles, called electrons. He determined the mass-charge ratio for an electron and came up with the "plum pudding" model of the atom . -
Marie and Pierre Curie
Discovered two radioactive elements, polonium and radium. -
Ernest Rutherford
He performed the gold foil experiment, determined that atoms contained a very small, positively charged core at the center, called this core the nucleus and came up with the nuclear model of the atom with electrons orbiting around the nucleus. -
Max Planck
Max used the idea of quanta (discrete units of energy) to explain hot glowing matter. -
Robert Millikan
He performed an "oil-drop" experiment, determined the charge of one electron and using the known mass-charge ratio, was able to calculate the mass on one electron (9.11x10^-28g). -
Niels Bohr
Developed the quantized orbit model of the atom and discovered that electrons can only reside in certain energy levels. -
Louis de Broglie
De Broglie discovered that electrons had a dual nature-similar to both particles and waves (particle/wave duality). He supported Einstein’s ideas. -
Erwin Schroedinger
Expanded the idea that electrons behaved as particles and waves, this developed the quantum mechanical model of the atom -
James Chadwick
The neutron was discovered using alpha particles which discovered a neutral atomic particle with a mass close to a proton. -
Glenn Seaborg
Glenn Seaborg synthesized 6 transuranium elements and suggested a change in the layout of the periodic table. -
Michael Faraday
Faraday coined term "electrolysis" as a splitting of molecules with electricity, developed laws of electrolysis. He himself was not a proponent of atomism and he studied the effect of electricity on solutions. -
Albert Einstein
Einstein published the famous equation E=mc 2. Also he proved that atoms actually exist. -
Lise Meitner
Lise conducted experiments verifying that heavy elements capture neutrons and form unstable products which undergo fission. This process ejects more neutrons continuing the fission chain reaction. -
Otto Hahn
Otto Hahn discovered fission in the nucleus of an atom. -
Indivisible solid sphere model
Democritus' theory, atom is the smallest particle of natter -
Plum Pudding Model
Thomson's idea that protons and electrons were contained in the nucleus. -
Planetary Model
The idea that electrons move around the nucleurs. -
Electron Cloud Model
The idea that electrons surrounded the nucleus. -
Quantum Mechanical Model
Max Planck's idea that electrons circled the nucleus in levels.
