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Atomic Theory

Explore the historical journey of atomic theory from Democritus' belief in indivisible atoms to Rutherford's discovery of the nucleus, tracing the scientific advancements that revolutionized our understanding 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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