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350
Aristotle 350 BC
Aristotle’s theory made a great law off all matter being made of the four elements: water, fire, air and eath. He also believed that there were four aspects to these elements: hotness, dryness, coldness, and moistness. Based on these thoughts fire would hold the characteristics of being dry and hot, water is wet and cold, air is hot and wet, while the earth is dry and cold. -
400
Democritus 400 BC
The first coherent atomic theory, Democritus explanied the idea to state that matter was made up of tiny particles which couldn't be seen by the naked eye. These particles where called 'atoms' which could not be divided to any more particles, The particles he belived where composed by the same substance but had slight change in shape, size, and weight. all atoms are very simmilar in their charecteristics but have a slight different in the properties around us. -
Antoine Lavoisier
the "father of modern chemistry," was a French nobleman extended in the histories of chemistry and biology. He called both oxygen and hydrogen and helped creat the metric system, put together the first general list of elements, and helped to reform chemical nomenclature. He was also the first to organize the thought that sulfur was an element not a compound. He discovered that, although matter may change its form or shape, its mass always remains the same. -
John Dalton
John Dalton achived to print his first published table of relitive atomic weights. there are about six elements to appear in this table, which are hydrogen, oxygen, nitrogen, carbon, sulfur, and phosphorus, and theatom of hydrogen asuumed to wehight 1. john dalton is alsdo credited for devboloping and creating the first offical coherent theory. -
D.Mendeleev
the creater of the fist perodic table, with an amount of 28 elements categorized by their valence electrons. He attamted to clasify the elements according to their chemical properties, he also noticed patterns that led him to advance his periodic table mendeleev was thoughtless of the eailer work on periodic tables going on in the 1860s. -
J.J. Thomson
1897, J. J. Thomson discovered the electron, a negatively charged particle more than two thousand times lighter than a hydrogen atom. In 1906 Thomson's plan that each atom had a number of electrons about equal to its atomic number. Since atoms are neutral, the charge of these electrons must be balanced by a kind of positive charge. Thomson proposed a 'plum pudding' model, with positive and negative charge filling a sphere only one ten billionth of a meter across. -
R. A. Millikan
mass of electron determined, Millikan calculated the force gravity would have on the droplet and then equaled that to the observed amount of charge that was required to suspend the droplet to determine the absolute charge of a particular droplet. When Millikan found out the force gravity had on the droplets he very soon realized that the amount of charge on each minutely affected the velocity of the fall. This was proof of a very small electron mass. -
H. Moseley
Atomic number determined, created the function of the X-ray spectra to help study and learn about the atomic structure. He figured out that some lines in the X-ray spectrum of each element moved the same amount each time you aded the atomic number by one.
Moseley's discoveries resulted in a more accurate and persious positioning of elements in the Periodic Table by closer determination of atomic numbers.In 1913, -
E. Rutherford
proton exactince, Before confirmation of the proton's existence in 1918 by Ernest Rutherford, the scientific community generally viewed the theory of protons with great speculation, ridiculing science enthusiasts who pursued the idea. Before Ernest Rutherford's work, it was Eugene Goldstein who, through extensive experimentation, believed he could prove the existence of the proton. Unfortunately, Goldstein's work was never completed, leaving the field open for Rutherford's experiments in 1918. -
J. chadwick
with Ernest Rutherford’s discovery of the positively-charged proton, it kind of looked to many physicists as if a almost complete model of the atomic structure was at hand.l, there also was the electron which was tiny and seemed to move like a solarsystem and the neucleus in the center.
