Atomic Theory Timeline by Alyssa Larson

• Democritus (460-370 BC) He was an Ancient Greek phliosopher who first suggested the exicstance of an ultimate particle. He formed an atomic theory for the cosmos. He used the word "atmos" to describe this particle. He is considered to be the "Father of Modern Science." (http://www.timelineindex.com/content/view/1228) (http://cstl-csm.semo.edu/mcgowan/ch181/atomhist.htm)
• Aristotle (384-322 BC) He believed in the four elements of air, earth, water, and fire. He considered the heavens to be an element as well. the also believed the no matter how many times you cut something in half you will always have a smaller piece of the remaining matter. (http://en.wikipedia.org/wiki/Aristotle) (http://cstl-csm.semo.edu/mcgowan/ch181/atomhist.htm)
• Johann Becher (1635-1682) and George Stahl (1660-1734) These two men developed a Phloogiston theory which over ruled chemistry between 1670 and 1790. Their theory was simply that if something burned it released phlogiston to the air. In which case the only thing you could see was the phlogiston. The only flaw with their theory was that when you are burning metals it only increases in mass. They resolved the problem by adding negative mass to phlogiston. (http://cstl-csm.semo.edu/mcgowan/ch181/atomhist.htm)
• Joseph Priestley (1733-1804) He discovereved the gas known today as "oxygen". He came to the United States in 1794. He was known by Americans for his political and theological writings, as well as his scientific contributions. (http://www.chemheritage.org/discover/chemistry-in-history/themes/early-chemistry-and-gases/priestley.aspx)
• Antoine Lavoisier (1743-1794) He discovered that water is made of hydrogen and oxygen. He proposed the Combustion Theory founded on sound mass measurements. He discovered the analytical balance that showed that chemical elements were neither created or destroyed, in fact they are simply combined into different compounds in chemical reactions. He also proposed the Law of Conservation of Mass. (http://cstl-csm.semo.edu/mcgowan/ch181/atomhist.htm) (http://www.chem.uic.edu/?lavoisier.htm)
• Joseph Louis Proust (1754-1826) He proposed the Law of Constant Composition in 1799. This law was strongly debated by Claude Berthollet (1748-1822). (http://cstl-csm.semo.edu/mcgowan/ch181/atomhist.htm)
• John Dalton (1776-1844) He proposed the Law of Multiple Proportions. After this he proposed the Atomic Theory in 1803. He explained that each chemical element is composed of atoms of a single, unique type, and chemically can not be altered or destroyed. They can combine to make a more complex structure formally known as a chemical compounds. (http://cstl-csm.semo.edu/mcgowan/ch181/atomhist.htm) (http://en.wikipedia.org/wiki/John_Dalton)
• Joseph Gay-Lussac (1778-1850) He announced the Law of Combining Volumes in 1808. He proved that at the same temperature and pressure, two volumes of hydrogen gas reacted with one volume of oxygen gas to produce two volumes of water. (http://cstl-csm.semo.edu/mcgowan/ch181/atomhist.htm)
• Amadeo Avogadro (1776-1856) He proposed what is commonly known as Avogadro"s Hypothesis in 1811. This law eplained that at the same temperature and pressure , equal volumes of gasesof gases contain the same number of molecules or atoms. This law goes hand in hand with Gay- Lussacs Law. (http://www.chemheritage.org/discover/chemistry-in-history/themes/the-path-to-the-periodic-table/avogadro.aspx) (http://cstl-csm.semo.edu/mcgowan/ch181/atomhist.htm)
• Robert Brown (1777-1858) He was Scottish botanist, he discovered the cell nucleus and cytoplasmic streaming. This was the first observation of the brownian motion. He also made many contributions to plant taxonomy. (http://en.wikipedia.org/wiki/Robert_Brown_(Botanist)
• Dimitri Mendeleev (1834-1907) He worked on the periodic table of elements which was developed in 1869. He arranged 63 elements by their atomic weights, and organized them into groups that have similar properties. If there was gaps he left them to be filled with future elements. (http://www.corrosion-doctors.org/Biographies/MendeleevBio.htm)
• J.J. Thomson (1856-1940) He discovered the electron through his work on cathode rays in 1897. He concluded that the electron was a component of all matter and calculated the charge to mass ratio for the electron. (http://cstl-csm.semo.edu/mcgowan/ch181/atomhist.htm)
• Robert Milligan(1868-1953) He decided that the unit charge of the electron in 1909 with his oil drop experiment. This allowed the calculation of the mass of the electron and the positively charged atoms. (http://cstl-csm.semo.edu/mcgowan/ch181/atomhist.htm)
• Ernst Rutherford (1871-1937) He found the nuclear atom as the result of the gold-foil experiment in 1911. He discovered that most of the mass and positive charge of an atom is concentrated in a very small fraction of its volume, which was assumed to be the very center. (http://www.rsc.org/chemsoc/timeline//pages/1911.html)
• Federick Soddy (1877-1956) He was a radiochemist who showed that radioactivity is due to the transmutation of elements. He proved the existance of isotypes of certain radioactive elements. (http://en.wikipedia.org/wiki/Federick_Soddy)
• Albert Einstein (1879-1955) His relativity was that the largest things in the universe, this opposed the quantom theory which deals with the tiniest thing we know as the particles of an atom. ( http://coraifeartaigh.files.wordpress.com/2008/07/einstein-1.pdf)
• Niels Bohr (1885-1962) He refined Rutherford's model by sowing different orbits in which electrons spin around the nucleus. He argued that each electron ha certain fixed amount of energy, which corresponds to its fixed orbit. The idea of electrons having a energy quantities(quanta)is known as the Quantom Theory. (http://www.daviddarling.info/encyclopedia/B/Bohr_atom.html)
• Henry Moseley (1887-1915) He discovered the energy of x-rays emitted by the elements increased with each successive element. In 1913 he stated that the relationship was a function of the positive charge on the nucleus which rearranged the periodic table. They now use the atomic number instead of atomic mass to show the progression of the elements. (http://cstl-csm.semo.edu/mcgowan/ch181/atomhist.htm)
• James Chadwick (1891-1974) He dicovered the neutron in 1932. This combined with Rutherford's idea eventually led to the discovery of the atomic bomb. (http://cstl-csm.semo.edu/mcgowan/ch181/atomhist.htm)
• Werner Heisenberg (1901-1976) He formulated one of the most eminent laws of the quantom theory, the uncertainty principle. This is occasionally is called the principle of inderminacy. (http://library.thinkquest.org/15567/bio/heisenberg.html)