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ATOMIC THEORY

ATOMIC THEORY. REVIEW. Democritus 460-370 BCE. Greek word atomos means indivisible all matter composed of tiny, solid particles properties of atoms determine properties of matter. Aristotle 384-322 BCE. matter composed of: 4 primary elements air water earth fire

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ATOMIC THEORY

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  1. ATOMIC THEORY REVIEW

  2. Democritus460-370 BCE • Greek word atomos • means indivisible • all matter composed of tiny, solid particles • properties of atoms determine properties of matter

  3. Aristotle384-322 BCE • matter composed of: • 4 primary elements • air • water • earth • fire • 4 secondary elements • wet • cold • dry • hot

  4. Aristotle384-322 BCE • argued against Democritus’ view of atoms • did not believe in concept of atoms • matter can be infinitely divided

  5. hydrogen gold Dalton1803 • Atomic Theory • All matter is composed of atoms. • All atoms of a given element are alike. • All atoms of different elements are different. • Atoms cannot be divided or destroyed. • Atoms combine in certain ratios to form compounds.

  6. Thomson1897 • discovered negatively charged particle later called electron • Plum Pudding Model • negatively charged particles (plums) IN • positively charged mass (pudding)

  7. Important people: Henri Becquerel First discovered radioactivity 1896 Marie Curie Isolated radioactive elements 1890’s Radioactivity

  8. Radioactivity • Act of emitting radiation spontaneously • Caused when unstable atoms undergo changes within their nuclei

  9. Three types of radioactivity • Alpha decay • Positive particle • Used by Rutherford • Cannot penetrate human skin • Beta decay • Negative particle • Mildly penetrating • Gamma decay • Neutrally charged ray • Highly penetrating

  10. Rutherford1911/1919 • discovered nucleus • 1911 • discovered proton • 1919 • positive charge • atom is mostly empty space with positive nucleus in center and electrons located around edge of atom

  11. RutherfordGold Foil Experiment

  12. close up of particles hitting gold foil Link to animation

  13. Bohr1913 • Solar System Model • electrons travel around nucleus in fixed path (orbit) • orbit based on energy level of electron • electrons move between orbits by gaining or losing energy

  14. Chadwick1932 • discovered the neutron • neutral charge • identical mass as proton

  15. Modern Model:Electron-Cloud • …the image of an electron moving so fast it appears to fill a region of space…

  16. Modern Model:Electron-Cloud • Louis de Broglie (1921) • suggested that waves could behave as particles and particles could behave as waves • Heisenberg Uncertainty Principle (1925) • cannot determine exact location of electrons • Shrödinger’s Equations (1926) • combined ideas into mathematical equations for determining location of electrons

  17. Modern Model:Electron-Cloud • Orbital is an electron density cloud • Densest area is where there is the greatest probability (90%) of finding an electron

  18. Each orbital has a different shape and maximum number: S: spherical-shaped P: dumb-bell shaped D: four-lobe-shaped F: six-lobe-shaped 2 electrons share the same orbital spinning in opposite directions Modern Model:Electron-Cloud Link to visual

  19. QUESTIONS?

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