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Atomic Theory

Atomic Theory. Scientific Method. Starts with a question:. In the Beginning…. 400 BC Democritus : Believed atoms were the smallest indivisible and indestructible forms of matter.

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Atomic Theory

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  1. Atomic Theory

  2. Scientific Method Starts with a question:

  3. In the Beginning… 400 BC Democritus: Believed atoms were the smallest indivisible and indestructible forms of matter.

  4. Aristotle: Disagreed. He thought all matter was continuous and part of the elements fire, earth, water, and air.

  5. 2000 years of darkness… 1690’s Scientific Experiments Law of conservation of mass- mass is not created nor destroyed

  6. 1808 Dalton’s Atomic Theory • Matter is made up of atoms • All atoms of an element are the same • Atoms cannot be subdivided, created, nor destroyed • Atoms combine in ratios to form compounds • In chemical reactions, atoms are combined, separated, or rearranged

  7. Dalton’s Model- 1808 Tiny, indestructible particles with no internal structure

  8. 1890- J.J. Thomson What is the nature of these mysterious, invisible carriers of electricity?

  9. Electrons are negative A cathode ray is deflected by a magnet. 4.2

  10. Electrons have mass Later proved by Millikan in 1916: 9.11 x 10^-31kg

  11. Electrons act like particles

  12. Summary In a sentence or two, describe the relationship between the cathode ray and electron.

  13. Thomson- 1890Cathode Tubes • Electrons are negatively charged • Electrons have mass • Electrons behave like particles • Exist in all atoms Plum-Pudding Model

  14. Unanswered Questions If electrons have such a small mass, what accounts for the higher mass? Atoms can’t be made solely out of electrons because atoms are neutral so something must balance it out.

  15. 1911- Ernest Rutherford

  16. Gold Foil Experiment

  17. Rutherford- 1911 • Mass concentrated in tiny core called nucleus • Electrons orbit the nucleus -If the nucleus is the size of marble, then the atom is the size of a football field Planetary Model

  18. Homework Atomic Timeline Show how scientists views have changed over time. -date -person/event -pictures

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