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History of Atomic Structure

History of Atomic Structure. Ancient Philosophy. Who: Democritus When: 400 BC Where: Greece What: believed that matter was made of 1 of 2 things. empty space small particles he named “atomos”. Reasoning: different kinds of atoms for each material

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History of Atomic Structure

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  1. History of Atomic Structure

  2. Ancient Philosophy • Who:Democritus • When: 400 BC • Where: Greece • What: believed that matter was made of 1 of 2 things. • empty space • small particles he named “atomos”. • Reasoning: different kinds of atoms for each material • Dog atoms, people atoms, tree atoms, water atoms

  3. Ancient Philosophy • Who:Aristotle • When: 350 BC • Where: Greece • What: believed that matter was continuous • made up of “hyle” • believed in the 4 earthly elements fire, earth, air, water – 1 heavenly element aether • Reasoning: best explanation for his observations

  4. Democritus Aristotle

  5. Alchemists • Who:European Scientists • When: 800 – 900 years ago • Where: Europe • What: Their work developed into what is now modern chemistry. • Why: Trying to change ordinary materials into gold.

  6. Alchemic Symbols

  7. John Dalton • When: 1800’s • Where: England • Why: Studied the works of others Lavoiser and Proust • Lavoiser – in ordinary chemical reactions, matter can be changed but can’t be created or destroyed (Law of conservation of Matter) • Proust – specific substances always contain elements in the same ratio by mass (Law of definite proportions)

  8. John Dalton • What: Described atoms as tiny particles that could not be divided. Thought each element was made of its own kind of atom. • Believed that atoms were simpler than particles of rocks, air, or dogs • Has 4 parts to his theory – two remain today

  9. Dalton’s Theory • All elements are composed of atoms – and atoms cannot be divided • All atoms of the same element have the same mass, and atoms of different elements have different masses • Compounds contain atoms of more than one element • In a particular compound, atoms of different elements always combine in the same way

  10. John Dalton Dalton’s Model – solid spheres of different masses for different elements

  11. J.J. Thomson • When: Late 1800’s • Where: England • What: Credited with the discovery of cathode ray (electrons). • Cathode – negative electrode • Anode – positive electrode • ray traveled from cathode to anode • Also discovered electron’s charge to mass ratio • Using a modified CRT discovered protons

  12. Thomson’s Experiment • Used a cathode ray tube. Noticed when charged particle beam bent

  13. Thomson’s Plum Pudding Model • Large positive sphere with negative charges imbedded in it • Positive balance negatives so net NO charge

  14. J. J. Thomson

  15. Bothe and Chadwick • When: 1930’s • Where: • What: First evidence of a third particle High energy particle with no charge

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