Atomic Theory Materiale liberamente creato da http://www.visionlearning.com Raffaele Nardella
The Early Days  - Thomson Model of the  atom  like a billiard ball  In 1897, J. J. Thomson’s discovery of the  electron   ...
The Early Days  -  Cathode Ray Tube   <ul><li>An electric current, through a vacuum tube, creates a stream of glowing mate...
The Early Days  -  Plum Pudding Model <ul><li>Thomson    Atoms like pieces of raisin bread </li></ul>Plum Pudding Model ....
The Early Days  -  Ernest Rutherford   <ul><li>Experiments with radioactive alpha particles (1908) </li></ul><ul><ul><li>a...
The Early Days  –  James Chadwick <ul><li>Discovering of a  subatomic particle : neutrons </li></ul><ul><ul><li>Reduction ...
The Early Days  –  Size of an Atom <ul><li>Atoms are very very small: </li></ul><ul><ul><li>empty space </li></ul></ul><ul...
Electron Shells – Niels Bohr   <ul><li>Modification to the atomic structure – Line Spectra </li></ul><ul><ul><li>matter he...
Electron Shells – Niels Bohr   <ul><li>Energy levels (electron shells) </li></ul><ul><ul><li>emitted light    the movemen...
Electron Shells – Niels Bohr   <ul><li>Key to Bohr's theory    the electron could only &quot;jump&quot; and &quot;fall&qu...
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Atomic theory

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Atomic theory

  1. 1. Atomic Theory Materiale liberamente creato da http://www.visionlearning.com Raffaele Nardella
  2. 2. The Early Days - Thomson Model of the atom like a billiard ball In 1897, J. J. Thomson’s discovery of the electron The atom was not &quot;indivisible&quot; as John Dalton suggested J. J. Thomson Raffaele Nardella
  3. 3. The Early Days - Cathode Ray Tube <ul><li>An electric current, through a vacuum tube, creates a stream of glowing material bending toward a positively charged electric plate  </li></ul><ul><li>The stream was made up of electrons carrying a negative charge </li></ul>Cathode Ray Tube Raffaele Nardella
  4. 4. The Early Days - Plum Pudding Model <ul><li>Thomson  Atoms like pieces of raisin bread </li></ul>Plum Pudding Model . Raffaele Nardella
  5. 5. The Early Days - Ernest Rutherford <ul><li>Experiments with radioactive alpha particles (1908) </li></ul><ul><ul><li>alpha particles </li></ul></ul><ul><ul><li>gold foil </li></ul></ul><ul><ul><li>bouncing straight back </li></ul></ul><ul><ul><li>positively charged dense core  nucleus </li></ul></ul><ul><ul><li>tiny solar system </li></ul></ul>. Raffaele Nardella
  6. 6. The Early Days – James Chadwick <ul><li>Discovering of a subatomic particle : neutrons </li></ul><ul><ul><li>Reduction of the repulsion between protons </li></ul></ul><ul><ul><li>Stabilization of the atom's nucleus. </li></ul></ul>. J. Chadwick Raffaele Nardella
  7. 7. The Early Days – Size of an Atom <ul><li>Atoms are very very small: </li></ul><ul><ul><li>empty space </li></ul></ul><ul><ul><li>spinning of electrons far from the nucleus (football field) </li></ul></ul><ul><ul><li>atomic number (z) = number of protons </li></ul></ul><ul><ul><li>atomic mass = number of protons and neutrons </li></ul></ul>http://facstaff.gpc.edu/~pgore/PhysicalScience/Atoms.html Raffaele Nardella
  8. 8. Electron Shells – Niels Bohr <ul><li>Modification to the atomic structure – Line Spectra </li></ul><ul><ul><li>matter heated  light </li></ul></ul><ul><ul><ul><li>light bulb: electric current heats a metal filament  absorbing the electrical energy  exciting the electrons </li></ul></ul></ul><ul><ul><li>white light through a prism  a continuous spectrum of colors </li></ul></ul><ul><ul><li>light from an excited element through a prism  only specific lines (or wavelengths) of light, called line spectra . </li></ul></ul>Continuous (white light) spectra Raffaele Nardella
  9. 9. Electron Shells – Niels Bohr <ul><li>Energy levels (electron shells) </li></ul><ul><ul><li>emitted light  the movement of electrons  electrons could not move continuously in the atom but only in precise steps </li></ul></ul><ul><ul><li>electrons occupy specific energy levels (electron shells) </li></ul></ul><ul><ul><li>atom excited  electrons can jump to higher levels </li></ul></ul><ul><ul><li>electrons fall back to lower levels, precise quanta of energy are released as specific wavelengths (lines) of light </li></ul></ul><ul><ul><li>electron shells  concentric circles around the nucleus </li></ul></ul>Niels Bohr Raffaele Nardella
  10. 10. Electron Shells – Niels Bohr <ul><li>Key to Bohr's theory  the electron could only &quot;jump&quot; and &quot;fall&quot; to precise energy levels, emitting a limited spectrum of light. </li></ul><ul><ul><li>electrons in the ground state , the lowest energy level possible (the electron shell closest to the nucleus). </li></ul></ul><ul><ul><li>electrons excited by adding energy to an atom (for example, when it is heated), </li></ul></ul><ul><ul><li>electrons absorb energy, &quot; jump &quot; to a higher energy level, and spin in the higher energy level </li></ul></ul><ul><ul><li>after a short time, electrons &quot; fall &quot; back to a lower energy level, giving off a quantum of light energy </li></ul></ul><ul><ul><li>levels have limits to the number of electrons </li></ul></ul>Raffaele Nardella

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