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465
B.C., The Idea of the Atom
Democritus around 465bc was wondering if he could cut somethng in half and then cut that in half again. Could you keep on cutting it forever? He reasoned that you would eventually come to the smallest grain of matter-the atom. The name comes from atomos which is greek for uncuttable. -
Dalton's Revision
A man by the name of John Dalton made a revison to Democritus's original theory. The revision of atomic theory came over two centuries later in the late 1700’s and into the early 1800's. His revision theory had three main parts. All matter is made of atoms. 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. Atoms are indivisible and indestructible. -
J. J. Thomson's Discovery
In 1897, J. J. Thomson made a discovery that needed to make a revision to the Atomic Theory. Dalton's atomic theory says that atoms are indivisible (meaning atoms cannot be broken any further into smaller particles) but because J.J Thomson proved that electrons exist, J.J thought that atoms are divisible. This changed Dalton's whole theory because Dalton's theory suggested that no subatomic particles were there but through the cathode-ray tube experiment he proved his theory. -
Ernest Rutherford's New Model
In 1909, Ernest Rutherford was responsible for the remarkable series of discoveries in the fields of radioactivity and nuclear physics. He discovered alpha and beta rays, were set forth from the laws of radioactive decay, and identified alpha particles as helium nuclei. Most important, he theorized the nuclear structure of the atom. -
Bohr's Development
Neils Bohr discovered lots of new new information about how the particles in atoms relate to each other. Neils Bohr discovered and founded the Bohr model which proves that the atom has a small positively charged nucleus. He developed an explanation of atomic structure that underlines regularities of the periodic table of elements. His atomic model included atoms that were built up of sucessive orbital shells of electrons. -
Modern Atomic Theory
Quantum Theory is the latest atomic theory. Many scientists have contributed to get to the modern-day theory that we are at today. Quantum theory has shown us that the electrons although they are particles also show some properties of waves. We know the atom as a nucleus that is surrounded by probability clouds. The clouds stand for the most probable locations of electrons. We still refer to these clouds as orbitals. The stature and shapes of the orbitals may be calculated mathematically.
