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John Dalton Dalton’s atomic theory has been the basis for chemistry for about 200 years. Although the theory that atoms where the smallest chemical object came thousands of years before, Dalton solidified it with careful testing and analysis, and then came up with an improved theory that stated; 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. This theory was proved by the test of time for all chemical reactions, but is not completely valid. Atoms can be destroyed, not by chemical means but nuclear reactions. Atoms can also have isotopes, which are atoms of the same element but of different masses, that still hold the same chemical properties. Dalton was an Englishman born in 1766. He was responsible for diligent research in many fields besides chemistry, having discovered color blindness, and weather. He lived until 1844. [] []

Henry Cavendish was born on October 10, 1731 in Nice, France. Cavendish attended Dr. Newcomb’s Academy in Hackney, England, and also had entered Peterhouse, Cambridge. After school he moved back to London, England to live with his father and built a laboratory. He never married and was so reserved that there was not much record of his social life accept with other scientists. Henry Cavendish had made his discovery in mostly electricity, and published a paper on the density of the earth. He is known for his discovery having to do with the nature and properties of hydrogen, specific heat of other substances, and various properties of electricity. [|**http://www.answers.com/topic/henry-cavendish**] [|**http://mattson.creighton.edu/History_Gas_Chemistry/Cavendish.html**] [|**http://www.notablebiographies.com/Ca-Ch/Cavendish-Henry.html**]
 * __ Henry Cavendish __**

Amedeo Avogadro Avogadro was an important chemist responsible for both ideal gas laws and mole ratios. In 1811 he created Avogadro’s law which states “equal volumes of gases at the same temperature and pressure contain the same number of molecules regardless of their chemical nature and physical properties". He discovered there are 6.022x1023 molecules of a substance in 22.41 liters of its gas no matter the substance, with the heaviest gasses as well as the lightest.   This lead him the create mole ratios allowing chemists to calculate the amount of a pure substance and relate masses of one element to one another. This is the basis for stoichiometry.  []

Losi.Mcneil.Atomic.Historytimeline.fall.2009