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450
Democritus
Democritus' theory was "everything is physically made op of atoms. He stated that atoms are indivisible and can never be broken down into pieces." His atomic model was just simply made of a sphere that is invisible, with no nucleus or electrons. He stated that that atoms are different in size, shape, and also temperature. He had drawn his model showing that atoms cannot be destroyed in any way or form possible. Democritus was born in 460 B.C and he died at more then a hundred years of age. -
500
Aristotle
Aristotle’s theory states that "all matter is made of the four elements: fire, water, earth, and air." He also stated that "there were four qualities to these elements: dryness, hotness, coldness, and moistness." He was born in 384 B.C and died in 322 B.C . -
John Dalton
Dalton is known as the father of atomic theory. His theory states 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." He was born on september 6, 1766 and died July 27, 1844. -
Henri Becquerel
Discovered radioactivity by accidentally putting crystal in the same drawer as a piece of photographic paper. He was going to do a different experiment, but it was canceled because of bad weather. When it started to clear up, he went to get his tools. He saw that the piece of material, which contained Uranium, could produce an image on the photographic paper even in the absence of light. -
Marie & Pierre Curie
Marie and Pierre's atomic theory was adopted in 1903 after they began a search for the source of the radioactivity. They discovered two elements, radium and potorium. The Curie's won a Nobel prize in physics for discovering the elements. Evidence that the model was correct was the fact that the elements they discovered were accepted to be in the Periodic Table. -
J. J. Thomson
Thomson's atomic theory is has multiple names, such as "Plum Pudding" and "Chocolate Chip Cookie" model. Thomson had first used the Cathode Ray Tube experiment, in which he had found a negative particle, called electrone. He had then done the chocolate chip cookie model. His atomic theory stated that the atom is not indivisible as it was of smaller pieces, protons and electrons. It also stated that "an atom consists of a sphere of positive charge with negatively charged electron embedded in it." -
Robert Millikan
Robert Millikan discovered the exact charge of the electron in his “Oil Drop Experiment”, further enhancing the model of J.J. Thomson. -
Ernest Rutherford
Ernest Rutherford performed an experiment where he shot alpha particles at gold foil, expecting them to pass right through. Some bounced back, however, and he formulated the planetary model, which showed that most of the mass of an atom was concentrated in the center (nucleus).Ernest Rutherford was the student of J.J. Thomson he was trying to prove Thomson’s model with his experiment, but ended up disproving it. -
Niels Bohr
He is responisble for the planetary atom. Bohr suggested that the electrons orbiting an atom could only exist at certain energy levels. The electrons had quantified amounts of energy using Planck’s Quantum theory. He proposed a new model of the atom where the electrons travel around the nucleus in orbits determined by their energy levels. -
James Chadwick
James Chadwick discovered the neutrally charged neutron, the discovery that ultimately led to the atomic bomb. He enhanced Bohr’s model by adding neutrons to the nucleus -
Quantum Model
Its' model of the atom explains its stability and like Bohr's Model, treats atoms as electrons surrounding a nucleus. The electrons, however, do not have a planetary orbit. Instead, the theory gives the location of an electron as a probability instead of showing it at a certain position.
