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HISTORY

Daily Inquiry – Wednesday, September 26 Create a “KWL” chart. Fill in the first two columns concerning what you know and what you want to know concerning ATOMS. HISTORY. The idea of atoms is very old.

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HISTORY

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  1. Daily Inquiry– Wednesday, September 26Create a “KWL” chart. Fill in the first two columns concerning what you know and what you want to know concerning ATOMS.

  2. HISTORY The idea of atoms is very old. Democritus (Greek, 400 BC) - said that things were made up of tiny, indivisible particles (atoms) – only an idea Aristotle - disagreed with Democritus’ idea – his opinion more popular. No evidence to support either idea.

  3. Three Important Laws • Law of Conservation of Mass (1789): • Mass is neither created nor destroyed. • Law of Definite Proportions (1797): • A chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound. • Example: water – 89% oxygen and 11% hydrogen

  4. Law of Multiple Proportions (1803): • if two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers • Example: Carbon and Oxygen • One compound – 1.33 g oxygen combines with 1.00 g carbon • Another compound – 2.66 g oxygen combines with 1.00 g carbon

  5. John Dalton (1808) English school teacher, wanted to explain the laws of conservation of mass, definite proportions and multiple proportions. His model is called the Atomic Theory.

  6. All matter is composed of extremely small particles called atoms. • Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties. • Atoms cannot be subdivided, created, or destroyed. • Atoms of different elements combine in simple whole-number ratios to form chemical compounds. • In chemical reactions, atoms are combined, separated, or rearranged.

  7. Some aspects of Dalton’s atomic theory have been revised. We now know that: • Atoms are divisible into even smaller particles. • A given element can have atoms with different masses.

  8. Structure of the Atom • JJ Thomson – 1897 • Matter composed of negatively charged particles called electrons

  9. “Plum pudding” model of atomic structure • Negative electrons were spread evenly throughout the positive charge of the rest of the atom

  10. Robert Millikan – 1909 • Oil drop experiment • Measured the amount of charge contained by the electron • 1.60 x 10-19 C

  11. Ernest Rutherford (1911)- • Atom composed of tiny positively charged region called nucleus. • Gold foil experiment

  12. Gold Foil Experiment

  13. Rutherford’s Model

  14. Niels Bohr (1913) - • Planetary Model • Electrons surround positively charged nucleus as planets orbit the sun.

  15. Bohr’s Planetary Model

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