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460
Democritus
Between 460-370 BC Democritus first proposed the existence of an ultimate particle. He used the word "atomos" to describe the particle. His theory states that these atoms are all individually created and cannot be separated, no matter what scientific procedures are applied. He also said, "there is no specific size that can be attributed to the various atoms and that they can differ depending on the various factors influencing them." -
John Dalton
John Dalton came up with the Law of Multiple Proportions. It led right to the discovery of the Atomic Theory in 1803. He also developed the mole and made up some the symbols for various elements. His atomic theory stated : " (1) all matter was composed of small indivisible particles termed atoms, (2) atoms of a given element possess unique characteristics and weight, and (3) three types of atoms exist: simple (elements), compound (simple molecules), and complex (complex molecules)". -
Henri Becquerel
In 1896, Henri Becquerel was studying the effect of x-rays on photographic film and he noticed some chemicals suddenly decompose and give off very pentrating rays. He won the nobel prize in 1903 for discovering Radioactivity. -
J.J Thomson
He identified the negatively charged electron in the cathode ray tube. Thomson is proposed the "plum pudding" model of the atom. The volume of the atom is composed primarily of the larger positive portion (the plum pudding). The smaller electrons (actually, raisins in the plum pudding ) dissapear throughout the positive mass to maintain charge neutrality. -
Marie& Pierre Curie
They spent much of their careers studying radioactivity and examining the particles and energy produced and in the process learnedmatter.They knew that the heavy element thorium was radioactive and found two new elements, polonium and radium. They were a husband and wife team. But Marie won Nobel Prizes in both physics and chemistry but Pierre didn't. Because girls are more smart. ;-) -
Robert Millikan
Robert determined the unit charge of the electron with his oil drop experiment at the University of Chicago. It allowed for the calculation of the mass of the electron and the positively charged atoms. The charge on a drop was always a multiple of 1.59 x 10-19 Coulombs. -
Ernest Rutheford
Rutherford came up with the idea that all of the positive charge and all of the mass of the atom took up 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. The model in the picture showed that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space. -
Niels Bohr
In 1922, Niels Bohr developed an explanation of atomic structure that shows the regularities of the periodic table of elements. He also had an atomic model. He thought that the way atoms give off radiation by electron jumping from an outer orbit to an inner one, it emits light. -
Quantum model
The Quantum model is the area where an electron may be located in. It also includes a nucleus that has neutrons and protons. The element that is my quantum model for is Beryllium. -
James Chadwick
This strapping lad discovered the neutron. The discovery of the neutron led directly to the discovery of fission and ultimately to the atomic bomb. He also proved that the atomic nucleus contained a neutral particle which was already discovered by Ernest Rutherford, but he just furthered the study of it. -
Aristotle
Aristotle came up with his Atomic Theory that stated; all matter is made up of these four elements: fire, water, earth, and air.He said there were four qualities to these elements wich are dryness, hotness, coldness, and moistness. He thought that however many times you cut a form of matter, you'll always have a smaller peice. He came up with his theory in 384-322 BC.
