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2 Theories of Matter
Discontinuous: Democritus; world was made up of empty space and tiny particles called atoms, which are indivisible
Law of Definite Proportions: for a substance the elements are always in the same ratio by mass
Dalton's Atomic Theory (1803)
1. Matter is composed of atoms that cant be broken down
2. All atoms of the same element are alike
3. Atoms of different elements are different
4. Atom can combine in different ratios to form compounds
Atom was an empty circle
noted under comstant comditions volumes of gas reactants and products were in small whole # ratios
Equal volumes of gases under the same temperature and pressure have equal number of molecules
J.J. Thomson (1897)
discovered electrons; placed the cathode ray tube in an electric field which caused the rays to bend toward the positive plate, and away from the negative plate; concluded rays were negatively charged
"oil drop experiment" determined the charge of electrons
1.60 x 10^-19 columb
mass of electron 9.11 x 10^-28 g
Rutherford "Gold Foil Experiment" (1911)
Alpha particle- helium nucleus
Came up with idea of an atom with a positiveky charged nucleus
discovered radioactivity by using Uranium rocks. The rocks in a dark drawer caused image on film
Rutherford (before 1909 experiment)- discovered 3 tupes pf radiation
Beta (high energy electrons)
Gamma Ray energy
modified Rutherford's model
proposed electrons were located in energy levels with a positive nucleus
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