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Democritus- ( 458- 370 B. C.E)
Democritus's theory of which everything comprised of atoms was controversial. He believed these atoms were physically indivisible, and so called them atoms. He believed that atoms are indestructible, that they have always been and always will be in motion; that there are an infinite number of atoms, and kinds of atoms, which differ in shape and size. Democritus theorized our basis of Atomic knowledge. http://www.vanosta.be/pcrphil_1.htm -
Antoine Lavoisier 1743-1794
The "father of modern chemistry", he was a French nobleman in the histories of chemistry and biology. He stated the first version of the law of conservation of mass, recognized and named oxygen, and hydrogen. He abolished the phlogiston theory and helped construct the metric system, He wrote the first extensive list of elements, and helped to reform chemical nomenclature. He discovered that, although matter may change its form or shape, its mass always remains the same.
http://www.princeton.edu/ -
Joseph Proust 1700's
Proust is best known as a chemist, particularly for his enunciation of the law of definite proportions. Proust’s law is that chemical substances only truly combine to form a small number of compounds, each of which are characterized by components that combine in fixed proportions by weight. His beliefs were were not at first accepted but later on were. -
John Dalton years 1808-1827
He believed that these Atoms were round particles which made up all matter and that each element differed with each other only by their weight.Dalton's theory was presented in the New systems of Chemical property which stated that all matter was composed of small indivisible particles termed atoms, atoms of a given element possesd unique characteristics and weight, and three types of atoms exist: simple , compound, and complex . www.biography.com
http://www.chemheritage.org/ -
plum pudding model
The plum pudding model proposed by J.J Thompson was the first to show electrons, but it excluded the nucleus. -
J. J. Thomson (1856-1940)
Thomson proposed the "plum pudding" model of the atom. In this model, the volume of the atom is composed primarily of the more massive (thus larger) positive portion (the plum pudding). The smaller electrons (actually, raisins in the plum pudding ) are dispersed throughout the positive mass to maintain charge neutrality.He found the negatively charged electron in the cathode ray tube in 1897. He deduced that the electron was a component of all matter and calculated the charge to mass ratio. -
J.J Thomson
The physicist j.j Thomson discovered the electron in a series of experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube. Thomson saw the deflection of the rays by electrically charged plates and magnets as evidence of "particles much smaller than atoms." He reasoned this as having a very large value for the charge-to-mass ratio.
http://www.chemheritage.org/ -
Robert Millikan (1868-1953)
Robert Millikan (1868-1953) determined the unit charge of the electron in 1909 with his oil drop experiment at the University of Chicago. Thus allowing for the calculation of the mass of the electron and the positively charged atoms.
e = 1.60 x 10-19 coulombs -
Ernst Rutherford (1871-1937)
Ernst Rutherford (1871-1937) proposed the nuclear atom as the result of the gold-foil experiment in 1911. Rutherford proposed that all of the positive charge and all of the mass of the atom occupied a small volume at the center of the atom and that most of the volume of the atom was empty space occupied by the electrons. This was a very radical proposal that flew in the face of Newtonian Physics. Also in 1920, Rutherford proposed the existence of the third atomic particle, the neutron.