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Atomic Theory

Atomic Theory. The history and structure of the atom. Atoms. Atoms are the fundamental building block of ordinary matter. They are smallest identifiable unit of an element. They are so small you can’t even see them with a microscope. . The Greeks. Democritus

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Atomic Theory

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  1. Atomic Theory The history and structure of the atom

  2. Atoms • Atoms are the fundamental building block of ordinary matter. • They are smallest identifiable unit of an element. • They are so small you can’t even see them with a microscope.

  3. The Greeks • Democritus • Proposed elements consist of tiny solid particles that cannot be subdivided.

  4. The History of the Atom • Dalton’s Atomic Theory (1808) • Each element is composed of tiny, indestructible particles called atoms. • All atoms of a given element have the same mass and other properties that distinguish them from the atoms of other elements. • Atoms combine in simple, whole-number ratios for form compounds. • Atoms of one element cannot change into atoms of another element. • In a chemical reaction, atoms change the way that they are bound together with other atoms to form a new substance.

  5. The History of the Atom • Scientists set out to prove Dalton’s theory • Late 1800’s J.J. Thompson’s Cathode Ray Experiment discovered the electron. • The cathode ray tube is a tube with partially vacuumed air. • In the tube there are two plates • one with a positive charge the other with a negative charge • When high voltage wires are attached an electrical charge is produced. • Rays are produced and can be seen when they hit a fluorescent material at the end of the tube.

  6. The History of the Atom

  7. The History of the Atom • What Thompson found • The streams of light traveled in straight lines • They were independent of the cathode plate material used • They carried a negative electrical charge. • These negatively charged particles he called Electrons. • The mass of these particles was much less than that of Hydrogen the lightest element. • This meant that there were smaller particles than the atom.

  8. Thomson Model 1904 • Plum pudding model

  9. The History of the Atom • Millikan’s Oil Drop Experiment (1909) • Found the Charge of the electron • Fine droplets of oil were sprayed into a drum with two electrical plates • The drops were allowed to fall through a small hole into the lower portion of the drum • The air was then bombarded with energy producing electrons • The negatively charged drops interacted with the negatively charged plate at the bottom of the drum • As the charge on the plate was varied the drops slowed, stopped, or reversed. • By measuring the voltage on the plate when the drops were stopped the charge of each electron would be found.

  10. The History of the Atom

  11. The History of the Atom • Rutherford’s Gold Foil Experiment (1909) • Rutherford shot alpha particles at a sheet of gold foil thinking that the particles would just past through. • He found that some of the particles were deflected . • This lead him to propose that the majority of the mass of the atom and the positive charge of the atom were all in the center of the atom NOT spread throughout. • There were large amounts of empty space in the atom.

  12. The History of the Atom

  13. Rutherford Model, 1911

  14. The History of the Atom • Nuclear Theory of the Atom • Most of the atom’s mass and all of its positive charge are contained in a small core called the nucleus. • Most of the volume of the atom is empty space, throughout which tiny, negatively charged electrons are dispersed. • There are as many negatively charged electrons outside the nucleus as there are positively charged particles (named protons) within the nucleus, so that the atom is electrically neutral.

  15. The History of the Atom • There was still unaccounted mass from the atom presented in Rutherford’s findings. • This mass was explained by James Chadwick as neutrons. • Neutrons are electrically neutral particles that also reside in the nucleus.

  16. The Atom

  17. Electron Cloud Model

  18. Beyond the Subatomic Particles • Scientists next question was what makes up protons, neutrons, and electrons? • The answer- Quarks! • Found by smashing protons together to break them apart. • Six different types.

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