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What is the smallest part of an element that still retains the properties of that element?

What is the smallest part of an element that still retains the properties of that element?. The beginning. The Indivisible Atom. World of Chemistry . http://www.learner.org/resources/series61.html. History. Democritus 2000 + years ago (400B.C.)

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What is the smallest part of an element that still retains the properties of that element?

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  1. What is the smallest part of an element that still retains the properties of that element?

  2. The beginning The Indivisible Atom

  3. World of Chemistry • http://www.learner.org/resources/series61.html

  4. History • Democritus • 2000+ years ago (400B.C.) • Came up with idea of the atom- means “indivisible” • Aristotle • (350 B.C.) didn’t believe in atoms • thought matter was continuous (thought you could keep dividing it) • Came up with first 4 elements

  5. Alchemy • In the early days chemistry was ruled by alchemy. • They believed that that could take any cheap metals and turn them into gold. • Alchemists were almost like magicians. • elixirs, physical immortality

  6. GOLD SILVER COPPER IRON SAND . . . . . . . . . . . . . . . Alchemy Alchemical symbols for substances… transmutation: changing one substance into another D In ordinary chemistry, we cannot transmute elements.

  7. Contributions of alchemists: • Information about elements • - the elements mercury, sulfur, and antimony were discovered • - properties of some elements • Develop lab apparatus / procedures / experimental techniques • - alchemists learned how to prepare acids. • - developed several alloys • - new glassware

  8. by 1700s, all chemists agreed: • on the existence of atoms • that atoms combined to make compounds

  9. They also knew: • The Law of Conservation of Mass

  10. John Dalton • Late 1700’s - John Dalton- England • Teacher- summarized results of his experiments and those of others • Combined ideas of elements with that of atoms in Dalton’s Atomic Theory

  11. learn this! Dalton’s Atomic Theory All matter is made of atoms. Atoms of same element have the same size, mass, and properties. (Different atoms of a specific element are different from any other element.) Atoms can’t be subdivided, created or destroyed. Atoms of different elements combine in whole number ratios to make compounds. In chemical reactions, atoms can be combined, separated, and rearranged.

  12. Some parts of Dalton’s theory were wrong: • atoms are divisible into smaller particles (subatomic particles) • atoms of the same element can have different masses (isotopes- atoms of the same type with different masses) • Most important parts of atomic theory: • all matter is made of atoms • atoms of different elements have different properties

  13. The Divisible Atom!

  14. In the beginning . . . Scientists noticed when current was passed thru a cathode ray tube-a light (or “ray”) was produced “ray” was attracted to a (+) and repelled a (-) Could be deflected by magnets Led scientists to believe there were negatively charged particles inside the cathode ray

  15. Discovery of Electron J.J. Thomson (1897) did more experimentation to actually make the discovery of the electron. His model was called “Plum-pudding” Thomson working with CRT

  16. Robert Milliken (1909) Using the “Oil –Drop” experiment Milliken determined the charge and calculated the mass of a single electron. Actual apparatus used.

  17. Scientists believed that. . . since atoms are neutral, something must balance the negative charge since an atom’s mass is so much larger than the mass of its electrons, there must be other matter inside an atom

  18. Discovery of Nucleus Ernest Rutherford discovered the nucleus by the famous Gold-foil experiment Alpha particles were Helium atoms go

  19. Ernest Rutherford-1911 Experiment: “gold foil” Aimed + charges (alpha particles) at foil Most particles went through indicating the atom is mostly empty space Some particles repelled indicating the atom has a dense positively charged nucleus

  20. Rutherford’s Model Eight years after the discovery of the nucleus, Rutherford refined his concept and stated that the nucleus contained positively charged “protons”

  21. Niels Bohr-1913 Believed the electrons were in definite orbits Orbits are also referred to as rings,clouds, shells, levels, or energy levels

  22. James Chadwick is credited with discovering the neutron in 1919 He used a method created by Irene Curie and her husband that detected particles given off by radioactive elements end

  23. Atomic History Timeline Activity • Using information from your notes, construct a timeline of atomic history. • Include dates, scientist names, description of model, and atomic model picture

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