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Copy of Atomic Structure Timeline

A timeline presenting radical ideas that shaped the way we see and understand the structure of atoms.
by

Richard Hubbell

on 30 March 2013

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Transcript of Copy of Atomic Structure Timeline

By Oscar Pimienta The Atomic structure Timeline The Atomic structure The present day diagram of the atom that we have come to know and understand wasn't made out of thin air. It was a journey that took us from the earliest models of the atom to the atom we know today. Let's take a look at this journey as different thinkers from different times each give us an idea as to what the atom is really like. Democritus is considered to be the father of modern science because of his contributions to the understanding of atoms. He was the first to actually use the word atom and he understood matter as the following:
1.All matter consists of invisible particles called atoms
2. Atoms are indestructible.
3. Atoms are solid but invisible.
4. Atoms are homogenous.
5. Atoms differ in size, shape, mass, position, and arrangement.
>Solids are made of small, pointy atoms.
>Liquids are made of large, round atoms.
>Oils are made of very fine, small atoms that can easily slip past each other. Democritus (400 BC) Developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up of sucessive orbital shells of electrons. Louis deBroglie 1924 Viewed electrons as continuous clouds and introduced "wave mechanics" as a mathematical model of the atom Erwin Schrodinger 1930 It is true that the atomic model has never been very certain. Even now more and more technological advances are allowing us to discover more about the atom and it's structure. What is certain is that the most common conception of the atom is from Bohr's model of the atom. And the model most used by scientists is the quantum mechanical model of the atom. Aristotle 300 BC (A bump in the road) While Democritus' atomic theory was well ahead of his own time, Aristotle did not accept this theory to be correct. Aristotle's ideas were not productive in the sense that they promoted the proper formation of the atomic structure, rather he made his own ideas as to what matter is made up of. He thought that all materials on Earth were not made of atoms, but of the four elements, Earth, Fire, Water, and Air. He believed all substances were made of small amounts of these four elements of matter. John Dalton 1803, 1805, 1808 Dalton said that elements consisted of tiny particles called atoms. He states an element is one of a kind (aka pure) because all atoms of an element are identical. All the atoms that make up the element have the same mass. All elements are different from each other due to differing masses. A compound is a pure (one of a kind) substance due to different elements bonded together. They are not easily separated from one another. Compounds have a fixed ratio of atoms. Each atom has its own characteristic weight, creating a weight ratio between elements. Also, his theory said that chemical reactions involve the rearrangement of combinations of atoms. His atomic theory stated the general information on the atom. Everything is made of atoms. All atoms of different substances have different weights. Robert Milikan/ Joseph John Thomson (1897) Millikan conducted the Oil Drop Experiment, in which he sprayed tiny oil droplets and had them fall through a small, charged hole into a closed area. The oil droplets now had a charge on them. He, then, introduced the area to an electric field. The charged oil particles now moved up and down at his whim. By observing the speed of the particles, he was able to find out the charge on a single electron: 1.6*10-19 Coulombs. J.J. Thomson discovered electrons and noticed that an atom can be divided through the implementation of his cathode ray experiment. Also, he concluded atoms are made of positive cores and negatively charged particles within it. He developed the Plum Pudding Model before the atomic nucleus was discovered. This model shows that the electrons are surrounded by a "pudding" of positive charges to balance the negative charges. Today, J.J. Thomson's discoveries have helped people to have a better understanding of the atom and its generic makeup. Max Planck 1900 Planck used the idea of quanta (discrete units of energy) to explain hot glowing matter. Ernest Rutherford 1911, 1915, 1918 Using alpha particles as atomic bullets, probed the atoms in a piece of thin (0.00006 cm) gold foil . He established that the nucleus was: very dense,very small and positively charged. He also assumed that the electrons were located outside the nucleus. Niels Bohr 1912 An indivisible model of the atom where it is merely one tiny particle. No knowledge of charges, but hooks were used to describe the grouping of atoms. The plum model made by Thomson with a positively charged base and negatively charged electrons on top of it. Developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up of successive orbital shells of electrons. This model of Bohr's atom is presented in the form of the planetary model with the implementation of orbits or shells that go around the nucleus. Planck's discoveries lead to the creation of a more mathematical model of the atom called the quantum mechanical model of the atom. This model shows the atom in a more unpredictable way. Rutherford developed a planetary model of the atom that resembles the planetary orbits in our solar system where the nucleus represents the sun and the electrons represent the planets. Rutherford also developed the nuclear model of the atom where the center of the atom is a nucleus with positive protons and negative electrons orbiting this cluster. Werner Heisenberg 1927 Described atoms by means of formula connected to the frequencies of spectral lines. Proposed Principle of Indeterminancy - you can not know both the position and velocity of a particle. James Chadwick 1932 Using alpha particles discovered a neutral atomic particle with a mass close to a proton. Thus was discovered the neutron. References http://www.dummies.com/how-to/content/atomic-structure-the-quantum-mechanical-model.html
http://library.thinkquest.org/C006669/data/Chem/atomic/development.html
http://www.universetoday.com/60137/democritus-model/
http://atomictimeline.net/index.php
http://the-history-of-the-atom.wikispaces.com/
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