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Lecture 4.1 & 4.2- Atomic structure

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Section 4.2 & 4.2 lecture for Honors & Prep Chemistry

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Lecture 4.1 & 4.2- Atomic structure

  1. 1. Lecture 4.1 & 4.2- Atomic structure Quiz 4 is this Friday Chapter 3 & 4 homework is DUE Friday
  2. 2. Everything in the world is made of less than 100 types of atoms called elements.
  3. 3. Everything in the world is made of less than 100 types of atoms called elements. They combine to make compounds like letters of the alphabet make words.
  4. 4. In a chemical reaction, one substance changes to another by reorganizing the way the atoms are attached to each other.
  5. 5. In 1803, John Dalton proposed a theory which accurately described and predicted chemical behavior. Dalton’s four postulates are still accepted today (with a few modifications)
  6. 6. Dalton’s Atomic Theory- 4 postulates All elements are composed of tiny indivisible particles called atoms.
  7. 7. Dalton’s Atomic Theory- 4 postulates All elements are composed of tiny indivisible particles called atoms. Dalton was wrong about the “indivisible” part, but the rest of this tenet is still fundamental to chemistry.
  8. 8. Dalton’s Atomic Theory- 4 postulates Atoms of the same element are identical. The atoms of any one element are different from those of any other element.
  9. 9. Dalton’s Atomic Theory- 4 postulates Atoms of different elements can physically mix together or can chemically combine in simple whole-number ratios to form compounds.
  10. 10. 4.1 Dalton’s Atomic Theory- 4 postulates Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element are never changed into atoms of another element in a chemical reaction.
  11. 11. Atoms are composed of protons, neutrons, and electrons.
  12. 12. Atoms are composed of protons, neutrons, and electrons. Protons and neutrons are found in the tiny nucleus of the atom.
  13. 13. Atoms are composed of protons, neutrons, and electrons. Protons and neutrons are found in the tiny nucleus of the atom. Electrons are found outside the nucleus. The cloud that they form is the majority of the atom’s size.
  14. 14. The number of protons in an atom determines the type of atom. Each element has a certain number of protons.
  15. 15. The electrons in an atom are involved in chemical reactions.
  16. 16. Protons and neutrons have similar mass 1 amu = 1 atomic mass unit = the mass of 1 proton or neutron
  17. 17. Protons and neutrons have similar mass 1 amu = 1 atomic mass unit = the mass of 1 proton or neutron Electrons have almost no mass
  18. 18. All of an atom’s mass is in the protons and neutrons in the relatively small nucleus.
  19. 19. All of an atom’s mass is in the protons and neutrons in the relatively small nucleus. All of an atom’s size is created by the electron cloud outside the nucleus.
  20. 20. Protons have a positive charge
  21. 21. Protons have a positive charge Electrons have a negative charge
  22. 22. Protons have a positive charge Electrons have a negative charge Neutrons have no charge Neutrons are neutral
  23. 23. Atoms are neutral because they have an equal number of protons and electrons.
  24. 24. Subatomic Particles
  25. 25. Sizing up the Atom Despite their small size, individual atoms are observable with instruments such as scanning tunneling microscopes. Iron Atoms Seen Through a Scanning Tunneling Microscope
  26. 26. Dearest students, The history of the evolution of atomic theory is always presented in order to impress upon students the importance of building upon current theories in order to get closer to the truth. In science, we honor the early “incorrect” theories because they led us to the heightened understanding that we have today. In keeping with this philosophy, we realize that our current understandings are just stepping stones towards the truth. With love, Mrs. Smith P.S. The following material will be very “lightly” tested. The next slides are for HONORS ONLY.
  27. 27. History of the atomic model Electrons a. In 1897, the English physicist J. J. Thomson discovered the electron in his cathode ray experiments. b. Electrons are negatively charged subatomic particles.
  28. 28. History of the atomic model a. Thomson performed experiments that involved passing electric current through gases at low pressure. The result was a glowing beam, or cathode ray, that traveled from the cathode to the anode.
  29. 29. History of the atomic model a. Cathode Ray Tube
  30. 30. History of the atomic model a. A cathode ray is deflected by a magnet.
  31. 31. History of the atomic model a. A cathode ray is deflected by electrically charged plates.
  32. 32. History of the atomic model a. Thomson concluded that a cathode ray is a stream of electrons. b. Electrons are parts of the atoms of all elements.
  33. 33. History of the atomic model Protons and Neutrons a. In 1886, Eugen Goldstein observed a cathode-ray tube and found rays traveling in the direction opposite to that of the cathode rays. He concluded that they were composed of positive particles. b. Such positively charged subatomic particles are called protons.
  34. 34. History of the atomic model
  35. 35. History of the atomic model a. In 1932, the English physicist James Chadwick confirmed the existence of the neutron. b. Neutrons are subatomic particles with no charge but with a mass nearly equal to that of a proton.
  36. 36. History of the atomic model a. J.J. Thompson and others supposed the atom was filled with positively charged material and the electrons were evenly distributed throughout. b. This model of the atom turned out to be short-lived, however, due to the work of Ernest Rutherford (1871–1937).
  37. 37. History of the atomic model a. Ernest Rutherford’s Portrait
  38. 38. History of the atomic model Rutherford’s Gold-Foil Experiment a. In 1911, Rutherford and his coworkers at the University of Manchester, England, directed a narrow beam of alpha particles at a very thin sheet of gold foil.
  39. 39. History of the atomic model a. Rutherford’s Gold-Foil Experiment
  40. 40. History of the atomic model a. Alpha particles scatter from the gold foil.
  41. 41. History of the atomic model a. Alpha particles scatter from the gold foil.
  42. 42. History of the atomic model
  43. 43. History of the atomic model The Rutherford Atomic Model a. Rutherford concluded that the atom is mostly empty space. All the positive charge and almost all of the mass are concentrated in a small region called the nucleus. b. The nucleus is the tiny central core of an atom and is composed of protons and neutrons.
  44. 44. History of the atomic model In the nuclear atom, the protons and neutrons are located in the nucleus. The electrons are distributed around the nucleus and occupy almost all the volume of the atom.

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