Minooka - Elements Part 2


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Minooka - Elements Part 2

  1. 1. Atoms and Elements Chemical Foundations
  2. 2. Atoms and Elements <ul><li>Element - Substances that can not be broken down further by ordinary chemical means </li></ul><ul><li>Atoms - The smallest particle of an element that retains the properties of the element </li></ul>
  3. 3. Postulates <ul><li>Elements consist of tiny particles called atoms </li></ul><ul><li>Atoms retain their identity in reactions </li></ul><ul><ul><li>They do not change into other types of atoms </li></ul></ul><ul><ul><li>Carbon stays carbon, Oxygen stays oxygen </li></ul></ul><ul><li>In a compound, atoms of two or more elements are combined </li></ul>
  4. 4. Atoms have parts <ul><li>Atoms are composed of protons, neutrons and electrons </li></ul><ul><li>All of the parts of the atom stay together as that atom in chemical reactions </li></ul>
  5. 5. Elements <ul><li>Elements represent the different types of atoms that are known </li></ul><ul><li>Come in solid, liquid and gas forms at earths normal temperatures </li></ul>
  6. 6. Top Ten
  7. 7. Most Abundant Elements on Earth
  8. 8. Most Common Elements
  9. 9. A collection of argon atoms.
  10. 10. Diatomic Elements
  11. 11. Nitrogen gas contains N 2 molecules.
  12. 12. Oxygen gas contains O 2 molecules.
  13. 13. Representation of NO, NO 2 , and N 2 O.
  14. 14. History of the discovery of the atom <ul><li>300 BC in Greece </li></ul><ul><ul><li>School of thought that matter is made up of tiny indivisible, invisible, indestructable, fundamental units of matter called atmos </li></ul></ul><ul><ul><li>Democritus of Abdera most well known atmostist. </li></ul></ul><ul><ul><ul><li>Did no experiments </li></ul></ul></ul><ul><ul><ul><li>No proof </li></ul></ul></ul><ul><ul><ul><li>philosopher </li></ul></ul></ul>
  15. 15. 1770’s <ul><li>Antoine Lavosier made observations and did experiments resulting in the Law of Conservation of Mass </li></ul><ul><li>Law of Conservation of Mass </li></ul><ul><ul><li>Matter can not be created or destroyed </li></ul></ul><ul><ul><li>Mass of materials before the chemical reaction is the same mass after the reaction </li></ul></ul>
  16. 16. 1799 - Proust <ul><li>Joseph Proust showed that the proportion by mass of the elements in a compound is always the same </li></ul><ul><li>Now called the Law of Definite Proportions </li></ul><ul><li>Part of our definition of a chemical - any substance with a definite composition </li></ul>
  17. 17. John Dalton <ul><li>English School Teacher </li></ul><ul><li>Alchemists were trying to change different metals into gold </li></ul><ul><li>Wanted to learn in what ratios that different elements combine </li></ul><ul><li>Performed experiments </li></ul><ul><li>Formulated theories to explain his observations </li></ul><ul><li>Proposed his theories in 1808 </li></ul><ul><li>Based on the Greek idea of the atom </li></ul>
  18. 18. Key idea - Dalton’s Atomic Theory <ul><li>All matter is made of indivisible, invisible, and indestructible particles called atoms </li></ul><ul><li>Atoms of the same element are identical </li></ul><ul><li>Atoms of different elements differ in their physical and chemical properties </li></ul>
  19. 19. Dalton’s Atomic Theory Con’t <ul><li>Atoms of different elements combine in simple whole number ratios to form compounds </li></ul><ul><li>Chemical Reactions occur when atoms are separated, joined or rearranged. Atoms of one element are NEVER changed into atoms of another element as a result of a reaction </li></ul>
  20. 20. 1870’s <ul><li>William Crooks developed the Crook’s Tube </li></ul><ul><ul><li>A tube with sealed gases and metal plates at the end </li></ul></ul><ul><ul><li>Run a current through the metal, and a glowing beam forms </li></ul></ul>
  21. 21. Schematic of a cathode ray tube.
  22. 22. 1897 - Sir J.J.Thompson <ul><li>Thompson proposed that the cathode ray formed in the tube is a stream of negatively charged particles </li></ul><ul><li>Key idea - ELECTRONS </li></ul><ul><li>Showed that all cathode rays are electrons regardless of the type of gas in the tube </li></ul><ul><li>Atoms have parts that are negatively charged </li></ul><ul><li>Since atoms are neutral, they must also have positively charged areas </li></ul><ul><li>Gave rise to the plum pudding model of the atom </li></ul>
  23. 23. Plum Pudding model of an atom.
  24. 24. 1886 - Goldstein <ul><li>E. Goldstein discovered a positively charged particle. </li></ul><ul><li>Called them PROTONS </li></ul><ul><li>Work was largely ignored </li></ul>
  25. 25. 1909 - Ernst Rutherford <ul><li>Rutherford physicist who experimented with the positively charged particle </li></ul><ul><li>He figured </li></ul><ul><ul><li>Atoms have no charge </li></ul></ul><ul><ul><li>Electrical charges are properties of matter </li></ul></ul><ul><ul><li>Electrical charges exist in single whole number units + or - (no fractions) </li></ul></ul><ul><ul><li>Electrical Charges cancel each other, therefore a + and a - together = neutral atom </li></ul></ul>
  26. 26. Rutherford’s experiment.
  27. 27. Results of foil experiment if Plum Pudding model had been correct.
  28. 28. Actual Results.
  29. 29. Rutherford’s model <ul><li>Key Idea -NUCLEAR ATOM </li></ul><ul><li>All of the mass of the positive particles (protons) is at the center region of the atom </li></ul><ul><li>Center region called the NUCLEUS </li></ul><ul><li>Electrons surround the nucleus in a “cloud” </li></ul>
  30. 30. 1913 - Niels Bohr <ul><li>Danish Physicist </li></ul><ul><li>Rutherford’s model did not work because the electrons are so small compared to the positive mass in the center of the atom </li></ul>
  31. 31. Bohr’s Atom <ul><li>There are certain energy levels in the space of the electron cloud that mathematically allow the electron to stay in the cloud (not crash into the nucleus) </li></ul><ul><li>Key idea - There are certain ORBITS in which an electron can travel around the nucleus without losing energy </li></ul>
  32. 32. Bohr’s atom con’t <ul><li>Suggested circular orbits </li></ul><ul><li>The farther away from the nucleus, the higher the energy level </li></ul><ul><li>Under normal conditions, electrons are arranged in the GROUND STATE. In the ground state, the electrons occupy the lowest energy level closest to the nucleus </li></ul>
  33. 33. All models have problems <ul><li>All models are not exactly correct, but they lead to further science and discovery </li></ul><ul><li>All have important key ideas </li></ul>
  34. 34. We now know… <ul><li>Atoms are made up of subparticles </li></ul><ul><li>Atoms are divisible, but not by ordinary chemical means </li></ul><ul><li>Atoms of elements can vary (isotopes) </li></ul><ul><li>Electrons reside in ORBITALS, not orbits </li></ul>