2.  Democritus (~400 BC) Greek philosopher who proposed that matter was made of tiny individual particles called “atomos” Believed atoms were indivisible and indestructible Approach was not based on the scientific method

3.  Period 5- Thursday, 10/22  Atomic Structure Test TOMORROW!  Protons, neutrons, and electrons  Average atomic mass calculations  Atomic History- Names, experiments, models, timeline  Use pgs. 9-14 in packet for review questions  key will be posted on shscience.net

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5.  John Dalton (1800) Proposed that atoms are tiny, indestructible particles, with no internal structure Known as the hard sphere model

6.  1) Matter is made up of tiny, indivisible particles called atoms 2) All atoms of a given element are identical 3) Atoms of different elements have different properties and masses Dalton’s Theory

7.  4) Different atoms combine in whole number ratios to form compounds 5) In a chemical reaction, atoms are separated, rearranged, or combined- but never changed into atoms of another element Dalton’s Theory, cont.

8.  Sir William Crookes (1875)

9.  Discovered the electron through an experiment with a cathode ray tube http://highered.mcgraw- hill.com/sites/0072512644/student_view0/chapter2/anima tions_center.html http://highered.mcgraw- hill.com/sites/0072512644/student_view0/chapter2/anima tions_center.html Proposed the “Plum Pudding Model” J.J. Thomson (1897)

10.  Performed the oil drop experiment to determine the charge on an electron ( 1.602 x 10 -19 coulombs) Robert Millikan (1909)

11.  Performed the Gold Foil Experiment Bombarded a thin piece of gold foil with a positive stream of alpha particles http://www.mhhe.com/physsci/chemistry/animat ions/chang_2e/rutherfords_experiment.swf 3 observations and 3 conclusions Known as the nuclear model Ernest Rutherford (1911)