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Law of Constant Composition
Law of Definite Proportions
- If a compound is broken down into its constituent elements, the masses of the constituents will always have the same proportions, regardless of the quantity or source of the original substance.
Joseph Proust -
Law of Conservation of Mass
The total mass present before a chemical reaction is the same as the total mass present after the chemical reaction; in other words, mass is conserved.
- Antoine Lavoisier -
Dalton's Atomic Theory
- Each chemical element is composed of extremely small particles that are indivisible and cannot be seen by the naked eye, called atoms. Atoms can neither be created nor destroyed.
- All atoms of an element are alike in mass and other properties, but the atoms of one element differ from all other elements.
- For each compound, different elements combine in a simple numerical ratio. John Dalton
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Discovering Electrons
Cathode rays are a type of radiation emitted by the negative terminal, discovered by passing electricity through nearly-evacuated glass tubes. The radiation crosses the evacuated tube to the positive terminal, the anode. Cathode rays can only be detected by light emitted by the materials that they strike, called phosphors.Another significant property of cathode rays is that they are deflected by magnetic and electric fields in a manner that is identical to negatively charged material. -
Law of Multiple Proportions
if two elements form more than one compound between them, the masses of one element combined with a fixed mass of the second element form in ratios of small integers. -
Plum Pudding Model
states that the electrons float in positively-charged material.
J.J. Thompson -
Discovery of Protons
experiments study the inner atoms using alpha particles, predicted that particles in an alpha beam would largely pass through matter unaffected, with a small # of particles slightly deflected. Particles would only be deflected if they have contact with electrons. Ernest Rutherford observed majority of alpha particles went through foil; some were slightly deflected, a small # were greatly deflected and another small number were thrown back in direction from which they came -
Discovery of Neutrons
a new type of radiation that consisted of neutral particles. It was discovered that these neutral atoms come from the nucleus of the atom.
James Chadwick (1891-1974)