CHEM 177L Study Guide - Benzene, Structural Formula, Hydronium
30 Oct 2014
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Document Summary
Democritus (460 370 bc): proposed atoms (indivisible) 17th century: atom concept re-invoked to explain gases. no chemistry. Theories = models: explanation, not provable, allow predictions: each element composed of small particles atoms, atoms of 1 type identical properties; atoms of different elements different, atoms of an element unchanged by chemical reaction. Atoms can neither be created nor destroyed: compounds formed form atoms combining in fixed ratios. Law of constant composition (1. 2) from postulate 4. Law of conservation of matter: in a chemical reaction, mass of the products is the same as the mass of the reactants postulate 3. Dalton deduced law of multiple proportions atoms can combine in different ratios to form different compounds. i. e. h2o and h2o2. Dalton: theory based on chemical reactions, no direct evidence of existence of atoms. Charged and + charged particles like charges repel, unlike charges attract. electrons cathode ray tubes originate from the negatively charged electrode or cathode.
