Created with Storyboard That for Ms. RoedigerImage Attributions: Democritus LACMA AC1993.213.2 (https://www.flickr.com/photos/wikimediacommons/16216393818/) by Fæ License: Attribution (http://creativecommons.org/licenses/by/2.0/) Cathode ray tube (https://www.flickr.com/photos/msittig/5901464050/) by Micah Sittig License: Attribution (http://creativecommons.org/licenses/by/2.0/) Portrait of Ernest Rutherford (1871-1937), Physicist and Chemist (https://www.flickr.com/photos/smithsonian/2551070939/) by Smithsonian Institution License: No known copyright restrictions (http://flickr.com/commons/usage/) HD.3A.002 (https://www.flickr.com/photos/departmentofenergy/10555706494/) by ENERGY.GOV License: United States Government Work (http://www.usa.gov/copyright.shtml) 1-3_Electron_orbitals (https://www.flickr.com/photos/fickleandfreckled/7927227544/) by fickleandfreckled License: Attribution (http://creativecommons.org/licenses/by/2.0/) JOHN DALTON'S ATOMIC TABLES (https://www.flickr.com/photos/summonedbyfells/13193085554/) by summonedbyfells License: Attribution (http://creativecommons.org/licenses/by/2.0/) Atom 3D Model (https://www.flickr.com/photos/prolithic/6616679503/) by ProLithic 3D License: Attribution, Non Commercial (http://creativecommons.org/licenses/by-nc/2.0/) diffracted hydrogen (https://www.flickr.com/photos/candace/315205005/) by cosmiccandace License: Attribution (http://creativecommons.org/licenses/by/2.0/) Democritus Dalton Thomson Rutherford Bohr Electron Cloud Model History of the Atom 400 BCETue Jan 01 1805Fri Jan 01 1904Sun Jan 01 1911Wed Jan 01 1913Sat Jan 01 2000LegendTime Break2303 Years and 347 Days400 BCETue Jan 01 1805Fri Jan 01 1904Sun Jan 01 1911Wed Jan 01 1913Sat Jan 01 2000LegendTime Break2303 Years and 347 DaysDemocritus used the word atomos, Greek for unbreakable, to describe the smallest parts of matter. His is an early atomic theory, though he lacked evidence. Five Statements of Atomic Theory, with evidence All elements are made of atoms that differ from one another. Atoms of the same element are identical. Atoms combine in whole number ratios. The cathode ray experiment helped Thomson realize that the atom could be divided into smaller parts, including a negatively charged part called the electron. He theorized that the positive part of the atom was like pudding with electrons embedded in it. With the gold foil experiment, Rutherford discovered the small, dense center of the atom and he named it the nucleus. By studying the spectral lines of hydrogen, Bohr theorized that electrons move at fixed energies, in paths he called orbits. His model described H perfectly. The modern idea of the atom suggests the 90% probability of "locating" an electron in mathematically-determined shapes called orbitals.