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History of Atomic Models

History of Atomic Models. The Atom. Early Greeks. Believed matter could be broken into four categories: Fire (Plasma) Earth (Solid) Water (Liquid) Air (Gas). Democritis. More than 2400 years ago. Philosopher- did no experiments. “can matter be broken down forever or is there a limit”

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History of Atomic Models

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  1. History of Atomic Models The Atom

  2. Early Greeks • Believed matter could be broken into four categories: • Fire (Plasma) • Earth (Solid) • Water (Liquid) • Air (Gas)

  3. Democritis • More than 2400 years ago. • Philosopher- did no experiments. • “can matter be broken down forever or is there a limit” • Called the smallest pieces ATOMOS (atom) meaning “not to be cut”.

  4. Democritis • Conclusions: • Atoms are small, hard particles • Atoms are made of the same material that differs in size and shape. • Atoms are infinite in number, always moving, and able to join.

  5. John DaltonEarly 1800’s • Found that gases combine as if individual particles • Chemist who did experiments, had an interest meteorology and studied air and properties of gases.

  6. John DaltonEarly 1800’s • Conclusions: • All elements are composed of atoms which are indivisible particles. • Elements contain atoms that are all the same for that element. • Atoms differ for different elements. • Compounds are formed by joining the atoms of two or more elements.

  7. J J Thomson 1897 • First hint that the atom is made of smaller particles. • He sent an electric current through a gas. The gas gave off rays that Thomson showed were negatively charged. • To this point in time, the uncharged atom was the only particle known. • Thomson concluded that a particle smaller than the atom had to exist.

  8. J J Thomson1897 • Thomson called the negatively charge particles “corpuscles” now called electrons. • Thomson model had a problem. The atom is known to have a neutral charge and now a negative particle is known to exist. The solution was that a positive particle has to exist to balance the negative charge. Thomson was unable to prove that the positive particle existed.

  9. JJ Thomson1897

  10. J J Thomson1897 • ‘Plum Pudding‘ model. Plum pudding is a rich, boiled or steamed pudding made with flour, suet, raisins, currants, citron and spices.

  11. Earnest Rutherford1908 • Rutherford was a British physicist who tested Thomson’s Model. • Gold Foil experiment. • Proposed that the atom has a small, dense, positively charged center called the nucleus.

  12. Rutherford 1908

  13. Rutherford1908 • The nucleus is tiny as compared to the whole atom. If a marble sits in the center of Heinz Field, the marble represents the nucleus while the stadium represents the whole atom. • The atom is mostly empty space.

  14. Neils Bohr1913 • Bohr improved the Rutherford model. • Definite orbits like planets around the sun. • Orbits are energy levels, of which there are 7.

  15. Werner Heisenberg1926 • Heisenberg was a German Physicist who proved that the position of the electron can never be exactly known. • Regions are known as orbitals where electrons might be found. • Electrons can jump from orbital to orbital. • Electron Cloud.

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