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Joseph Proust
Proposed the Law of Constant Composition in 1799. States that when compounds are analysed into their constituent parts they always contains the same proportions of their elements by weight. -
Period: to
Scientists' view of how the Atom has changed through the ages.
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John Dalton
Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass. Dalton believed that all matter is made of atoms. Atoms are indivisible and indestructible. All atoms of a given element are identical in mass and properties. Compounds are formed by a combination of two or more different kinds of atoms. A chemical reaction is a rearrangement of atoms and atoms can be neither created nor destroyed. -
Amedeo Avogado
Proposed Avogadro's Hypothesis in 1811. The hypothesis states that at the same temperature and pressure, equal volumes of gases contain the same number of molecules or atoms. -
Dmitri Mendeleev
He proposed the periodic law and devleoped the first periodic table in 1869. Medeleev's table was arranged according to increasing atomic weight and left holes for elements that were yet to be discovered -
JJ Thomson
JJ Thomson totally changed the view of an atom by discovering electron. Thomson's atomic theory suggested that the atom is not indivisible as it was of smaller pieces-electrons and protons.
He also suggests that an atom consists of a sphere of positive charge with negatively charged elctron embedded in it. The positive and the negative charges in an atom are equal in magnitude, due to which an atom is electrically neutral. It has no over all negative or positive charge. -
Marie Curie
Studied uranium and thorium and called their spontaneous decay process radioactivity. She and her husband Pierre also discovered the radioactive elements polounium and radium -
Hans Geiger
In 1911, he devised the first version of the Geiger counter to count the number of alpha particles and other ionising radiation. With the aid of other radiation detectors, he used his counter in early experiments that led to the identification of the alpha particles as the nucleus of the helium atom. -
Ernest Rutherford
Rutherford 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 atoms 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. Although positive particles had been discussed for some time, it was Rutherford in 1920 that first referred to the hydrogen nucleus as a proton. Also proposed the 3rd atomic particle, the neuton -
Niels Bohr
Developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up of sucessive orbital shells of electrons. -
Entrico Fermi
He conducted the first controlled chain reaction releasing energy fro the atoms nucleus.
