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What does an atom look like? How did scientists figure out what it looks like? Truemper 2016 Atomic Theory Truemper 2016 Democritus Smallest piece of all matter is not divisible He named the smallest piece of matter “atomos,” meaning “not to be cut.” Truemper 2016 Truemper 2016 John Dalton • • • • 1760-1844 Father of Modern Atomic Theory matter is made of atoms atoms in an element are identical different elements have different atoms atoms maintain their mass even in a chemical reaction Truemper 2016 J.J. Thomson 1897 Truemper 2016 When a magnet was placed near the beam of light, it separated into two parts Truemper 2016 When a magnet was placed near the beam of light, it separated into two parts Truemper 2016 Thomson Model Where did they come from? • This surprised Thomson, because the atoms of the gas were uncharged. Where had the negative charges come from? Truemper 2016 Thomson Model Proposed a model of the atom that is sometimes called the “Plum Pudding” model. a sphere with negatively charged electrons scattered. Truemper 2016 J.J. Thomson 1897 Hear Thomson talk the Electron discovered electrons (charged particles) Truemper 2016 Truemper 2016 Rutherford 1911 Using atoms to see what is inside of other atoms Truemper 2016 Rutherford Truemper 2016 Rutherford Experiment Molecular Expressions Truemper 2016 Rutherford’s experiment: Discovery of the Nucleus – Most of positively charged particles Rutherford shot at the gold foil passed right through without changing course at all. – However, some did bounce away from the gold sheet as if they had hit something solid. – He knew that positive charges repel positive charges. Rutherford found the Nucleus Truemper 2016 Rutherford’s model A nucleus in the center, with electrons moving around in the open space Truemper 2016 • 1) Most of the volume of the atom is ... empty space Truemper 2016 2) Virtually all mass atom found in ... ... the nucleus Truemper 2016 3) Strong, positive charge in the center of atom Truemper 2016 Relative Sizes in the Atom Truemper 2016 Did you know ... If the atom were the size of a football stadium, the nucleus would be the size of a.... Truemper 2016 .... a marble!!! Truemper 2016 Truemper 2016 Bohr Model • Electrons move in definite orbits around the positive nucleus • Like the planets orbiting the sun. • These orbits, or energy levels, are located at certain distances Truemper from2016the nucleus. Truemper 2016 Chadwick discovers the nucleus has neutrons Truemper 2016 Truemper 2016 Truemper 2016 Modern View of the Atom Electron Cloud “Wave” Model Truemper 2016 Electron Cloud Model • According to the theory of wave mechanics, electrons do not move about an atom in a definite path, like the planets around the sun. Truemper 2016 Schrodinger and the Electron Cloud: • Electrons whirl about the nucleus billions of times in one second • Location of electrons depends upon how much energy the electron has. Truemper 2016 Electron Cloud: Depending on their energy they are locked into a certain area in the cloud. • Electrons with the lowest energy are found in the energy level closest to the nucleus • Electrons with the highest energy are found in the outermost energy levels, farther from the nucleus. Truemper 2016 NOVA scienceNOW Amazing Atoms PBS.mp4 Truemper 2016 Atomic Theory Song by Veritasium Truemper 2016 Indivisible Electron Greek X Dalton X Nucleus Thomson X Rutherford X X Bohr X X Wave X X Truemper 2016 Orbit Electron Cloud X X
