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History of the Atomic Theory
Transcript of History of the Atomic Theory
everything is composed of atoms,
which are indivisible,
there is empty space between atoms,
they are indestructible,
they are always in motion, and
there is an infinite number of atoms with infinite shapes and sizes 1766-1844 Dalton 460BC-370BC Studied the ratios in which elements combine in chemical reactions Democritus was very devoted to his studies. One
story told that he even blinded himself so as not to be distracted by things unrelated to his pursuits. Dalton's Atomic Theory 1. All matter is made of atoms. Atoms are indivisible and indestructible.
2. All atoms of a given element are identical in mass and properties.
3. Compounds are formed by a combination of two or more different kinds of atoms.
4. A chemical reaction is a rearrangement of atoms. http://en.wikipedia.org/wiki/Democritus#Philosophy_and_science
http://en.wikipedia.org/wiki/Eugen_Goldstein J.J. Thomson 1856-1940 When Dalton experimented, he often
used inaccurate instruments causing many of his colleagues to question his results. He trusted his mind rather than his hands. However historians who have tested his experiments have confirmed his skill and precision. Dalton's Atomic Model Ernest Rutherford Rutherford's Gold Foil Experiment:
Rutherford shot an alpha particle ray through gold foil in order to test Thomson's plum pudding model. The ray should have gone through the foil only slightly deflected. Instead the ray bounced off of some unknown particle and was greatly deflected in some areas. This lead Rutherford to create his atomic model. How the ray should have been deflected (according to the plum pudding model): How it was actually deflected: 1871-1937 Ruthorford is the only Nobel Prize winner to have conducted his most famous work after receiving the award. Robert A. Millikan Eugen Goldstein James Chadwich Niels Bohr Erwin Schrodinger Hantaro Nagaoka Louis de Broglie Max Planck Albert Einstein 1892-1987 In 1924, De Broglie theorized that all matter, not just light, had a wave-like nature. This was later proved by Davisson and Germer. 1905- Einstein theorized that light can act as if were made on discrete, indepentent particles of energy, which he called light quanta. This explained how light could eject electrons from metals. Thomson's Model Thomson was credited with the discovery of the isotope and electron. He used the cathode ray to pass electric rays through a test tube at low pressure. He put a positive and a negative plate in the test tube, when we passed the ray in between them, it moved closer to the positive plate, even when the plates were reversed. This showed that the cathode ray was negatively charged. His “plum-pudding” model was that the electrons were embedded in the positive charge like plums in a plum pudding, even though the electrons could move around. Also in 1905 Thomson discovered the radioactivity of potassium; in 1906 he showed that hydrogen has only one electron. 1885-1962 2. Proved Kenetic energy 1. Redid the Principle of Relativity so that it more carefully considered time and called this new theory the theory of relativity. 3. E=mc2
energy=mass time the speed of light squared He theorized that the electrons traveled in orbits around the nucleus of the atom, called the Bohr Model. In the Bohr Model was based off of Rutherford’s model. He says that the atom is made up of a positively charges nucleus with electrons that orbit around the nucleus, and electrostatic forces hold the atom together. Einstein also: 1891-1953 Chadwick discovered a previously unknown particle in the atomic nucleus. This has come to be known as the neutron because of its lack of electric charge. 1865-1950 In 1904, Nagaoka developed an early planetary model of the atom. Nagaoka's model was based around an analogy to the explanation of the stability of the Saturn rings Millikan performed an oil-drop experiment to find the charge of a single electron. Thomson had already created the charge-to-mass ratio but neither the charge nor the mass of an electron was known. He was successful and won a nobel prize. What the world didn't know was that Millikan wasn't the only one to work on the experiment. His graduate student, Fletcher, also deserved credit and part of the prize. However, in exchange for claiming full authorship on a related topic in his dissertation, Fletcher gave all the credit to Millikan. He kept his secret until his death. 1858-1947 1868-1953 The Oil-Drop Experiment
Millikan sprayed oil inside an upper chamber of an appartatus he created for this experiment. He let the drops fall through a screen into the lower chamber and measured their velocity with a microscope. He them used a formula to find their mass.
Next he iodized the air, allowing some of the droplets to catch electrons. He attached a battery to the bottom so that the negatively charged drops were repelled from the battery and hung in the air.
This process allowed him to create a formula that told him a single electron's charge. Chadwick discovered a previously unknown particle, which he named neutron. Planck's law describes black body radiation. He proposed that electromagnetic radiation was emitted in quanta. He solved the eltraviolet catastrophe (balck curve) it eas a major problem in "classic" physics. He also was helped form quantum mechanics. Chadwick smashed alpha particles into beryllium, a rare metallic element, and allowed the radiation that was released to hit a sheet of paraffin wax. When the beryllium radiation hit hydrogen atoms in the wax, the atoms were sent into a detecting chamber. Only a particle with almost the same mass as a hydrogen atom could effect hydrogen like that. The experiment results showed a collision with beryllium atoms would release massive neutral particles, which Chadwick named neutrons. The Wave Equation describes how the wavefunction of a physical system evolves overtime. We can thank Schrodinger for the quantum mechanical model of the atom (the annoyingly confusing probablity of where an electron can be found). 1850-1930 He experimented with discharge tubes, and named the light emissions kathodenstrahlen, or cathode rays. He discovered many things about cathode rays. These things actually helped to identify them as subatomic particles, electrons. He found that they emitted perpendicularly from a metal surface and carried energy. He found that the tube with a perforated cathode emitted a glow at the end of the cathode. He also found that there is another ray that travels in the opposite direction of the ray that travels towards the positively-charged anode. He called these rays canal rays; they are composed of positive ions. He also used discharge tubes to investigate comets. He found that if you place a small glass or iron in the path of a cathode ray that it would make secondary emissions to the sides, making a comet’s tail. 1887-1961