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340
Aristotle's Contribution
Aristotle believed that all matter was made up either of water, air, earth, and fire, or combinations of these four elements, with the exception of stars and planets which were made of aether. Aristotle’s theory of matter has been proven wrong, as many more elements have been discovered since. -
400
Democritus's Contribution
Hypothesized that all matter (plus space and time) is composed of tiny indestructible units, called atoms. They remain unchanged, but move about in space to combine in various ways to form all macroscopic objects. For example, sweet things were made of smooth atoms, and bitter things were made of sharp atoms. While Democritus performed no experiments, his theory was kept alive by the Roman poet Lucretius which survived the Dark Ages. -
Antoine's Contribution
The first breakthrough in the study of chemical reactions resulted from the work of the French chemist Antoine Lavoisier. He found that total mass of the products of a chemical reaction is always the same as the total mass of the starting materials consumed in the reaction. His results led to one of the fundamental laws of chemical behavior: the law of conservation of matter. Atoms are neither created nor destroyed in a chemical reaction merely manipulated. -
John Dalton's Contribution
All atoms are indivisible and he believed all atoms of the same element were the same. Also, compounds form when two or more different types of atoms bond chemically -
Michael Faraday
Studied the effect of electricity on solutions, created the term "electrolysis" as a splitting of molecules with electricity, developed laws of electrolysis. -
Henri Becquerel
While studying the effect of x-rays on photographic film, he discovered some chemicals spontaneously decompose and give off very pentrating rays. -
J.J Thompson's Contribution
Thompson discovered the electron through his experiment in which he used magnets to manipulate the electrical discharge in a cathode ray tube. He concluded from the bendeing of the subject that the particles (electrons) have a negative charge. He also devised the "plum pudding model" to represent atoms as spheres which has an overall positive charge with little negative electrons randomly appearing throughout. -
Max Planck's Contribution
Introduced the concept of ‘quanta’ of energy. These are small ‘packets’ that can only hold certain, prescribed amounts of energy. This was known as "Quantum Theory". -
Albert Einstein's Contribution
Einstein was able to identify atoms by observing the slight and various vibrations/movements of them. By explaining what he called Brownian motion he physically proved atoms exist. Also, the equation "e=mc^2" -
Ernest Rutherford's Contribution
Ernest discovered the nucleus of the atom through his "Gold Foil" experiment. He shot a stream of aplha particles at a sheet of gold foil, expecting them to go right through the foil. However, some particles bounced back. This was described as being as likely as a cannon ball being shot at a piece of tissue paper and the cannon ball bouncing off. In conclusion, the discovery of the nucles, a concentrated center of the atom, occurred. -
Robert Millikan's Contribution
Performed an "oil drop experiment" that determined the charge (e=1.602 x 10 -19 coulomb) and the mass (m = 9.11 x 10 -28 gram) of an electron. -
Niels Bohr's Contribution
Bohr accurately proposed that there was a central nucleus with electrons circling in rings. He believed that electrons fly around in orbits surrounding the nucleus, but that there are limits to where they can be. (Electron Cloud Model) He used the example of walking up a staircase, for one can walk on the flat part of the stairs but not on the risers. Basically, there are physical limits for atoms too. -
James Chadwick's Contribution
He discovered the neutron. By observing a previous experiment he came to the conclusion that the atom contained neutral particles (neutrons). He believed that neutrons have the same mass as protons, which accounted for more of the mass of the atom and allowed the masses (the known mass of an atom and the known mass of its particles) to match. -
Glenn Seaborg
Synthesized 6 transuranium elements and suggested a change in the layout of the periodic table. -
Erwin Shrödinger's Contribution
The Schrödinger model describes the probability that an electron can be found in a given region of space at a given time. This model no longer tells not where the electron is; it only where it might be.
