Atoms structures of, properties of, how they affect each other, history of Chapter 18 Ancient Greeks • Philosophers • Democritus –matter is discrete, not continuous, could not get a smaller piece • Leucippus called it atomos, Late 1700s Dalton Atomic Theory Behavior of matter • • • • Tiny indivisible particles called atoms Atoms of the same element are identical Can combine to form compounds Chemical reactions occur when atoms are separated, joined, or rearranged, but atoms of one element are not changed into atoms of another by a chemical reaction Late 1800sThompson • 1898 discovery of the Electron • Plum Pudding model-spherical blob of + and – charges inside. Raisins in pudding • Basic unit total plus charges = total – charges *means atoms are electrically neutral 1896 Becquerel discovered radioactivity -Uranium • Put uranium by photographic plates • The plates were exposed and he had pictures of the rocks. • Radioactivity is found in many basic elements • Alpha Αα • Beta Ββ • Gama Γγ Early 1900s Rutherford (Thomson’s student) famous experiment • 1911 mainly studying radioactivity • Gold foil experiment –when alpha particles (protons) were aimed at a piece of gold foil surrounded by a fluorescent screen, most passed through and a few particles were deflected. The greatly deflected action was not expected • Concluded that most passed through because the mass and positive charges were concentrated in one spot in the atom. The rest was empty space and passed through easily (most of it was empty space) • Called this the nucleolus . This is the part of the atom that was deflected instead of passing through the gold foil and was small compared to the size of the atom. • Electrons were charged, randomly arranged around the nucleolus in random motion. They moves so that they were not pulled into the nucleolus.