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450
Aristotle (460 B.C.E.)
Aristotle did not believe in the atomic theory. He developed the theory that all matter consisted of the four elements; earth, air, water, and fire. He also proposed the four qualities dryness, hotness, coldness, and moistness.
Soll, Ivan. "Aristotle." World Book Student. World Book, 2014. Web. 28 Feb. 2014. -
450
Democritus (380 BCE)
Democritus argued that the world consisted of an infinate number of atoms mmoving in an infinate void. Atoms were invisible and indivisble particle of matter and differ in size, shape, and position. He believed everything in the world is made up of different combinations of atoms. Democritus disputed the claim of Parmenides that empty space cannot exist. He used the "Theory of Atomism" - a theory about the subsances of the world to support his claims. -
John Dalton
John Dalton advanced the atomic theory by saying that they're are many types of atosm. He had five claims: 1. Pure elements consisted of particles called atoms. 2. Atoms of an element are all the same. 3. Atoms of different elements told apart by their weight. 4. Atoms of elements combine to breate chemical compounds. 5. Atoms cannot be created or destroyed, He supported his findings with his own theory called Dalton's Law. -
J.J. Thomas
He stated that stoms consisted of rings of negative electrons emebded in the sphere of positive charge. Dalton belived that the positive charges balance to make a neutral arom. The mass id the atom is due to the nucleus. He found they're 1840 electrons in a hydrogen atom. He used cathodes to determine the negativly charged particles. -
Ernest Rutherford
Rutherford discovered the nucleus and the positivey charged particles that he called protons. He conducted the "Gold Foil Experiment" which used charged radiation to bombard the atom and watched to see where the radiation particles went. The particles began to glow. -
Niels Bohr
Bohr believed that the electrons of an atom traveled in shells or on certain energy levels around the nuclues. He said that chemical propertis were determined by the number of electrons. He developed the theory of hydrogen spectrum to show that only a certain amount of energy is allowed in an atom. -
Erwin Schrodinger and Werner Heisenberg
Together, they formulated the uncertainty principle which says that you cannot know by measurement the position and momentum of a particle simultaneously. Particles and fields undulate and jump between all possible values consistent with the quantum uncertainty. Atoms were now visualized as a nucleus surrounded by a cloud of electrons distributed according to a wave pattern by the Schrodinger equation.
