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Atomic Structure

Atomic Structure

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Atomic Structure

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  1. Atomic Structure Unit 4 Expected test date: 28-Oct-08

  2. The Atom • The smallest particle of an element that still retains the properties of the element. • Atoms are much too small to see • What does it look like?

  3. Subatomic Particles • Atoms are made of smaller particles • Protons • Neutrons • Electrons

  4. The Structure of Atoms

  5. The Philosophers • Ancient Greeks • Formed ideas of nature based on their experiences • Did no experiments, just thought

  6. The ancient idea • Everything made of : Fire Earth Air Water

  7. Democritus(460 – 370 B.C.) • Greek philosopher (not scientist) • Named the atom • Different kinds of atoms have different sizes and shapes. • Apparent changes in matter result from changes in the groupings of atoms and not from changes in the atoms themselves.

  8. John Dalton(1766-1844) • First atomic theory • All matter is composed of atoms. • All atoms of a given element are identical and different from those of any other element. • Atoms combine in simple whole number ratios to form compounds. • In a chemical reaction, atoms are separated, combined, or rearranged.

  9. Early Theories of Matter • Workbook: Page 19 • Numbers 1 through 12

  10. By the late 1800s… • Cathode ray tube invented

  11. JJ Thomson(1897) • Cathode rays made of particles smaller than atoms • First subatomic particles • Discovered the electron • Plum pudding model of the atom

  12. Electron • Charge of negative one (-1) • Almost no mass (1/1840 mass of proton) • Exists in the empty space around the nucleus

  13. Questions raised by Thomson • If electrons are particles smaller than atoms, are there other particles? • What makes up most of the mass of the atom? • If electrons are negatively charged, why are atoms neutral?

  14. Plum pudding model • Atom is a sphere • Positive charge is evenly distrubuted • Negatively charged electrons spread randomly through the sphere

  15. Let’s draw that • Workbook: Page 20 • Number 4

  16. Ernest Rutherford(1911) • Aimed a beam of “alpha particles” at a thin gold foil • The beam made a bright spot on a fluorescent screen

  17. Florescent Screen Lead block Uranium Gold Foil

  18. What Rutherford expected

  19. What Rutherford expected α α α α α α

  20. What Rutherford saw

  21. + What Rutherford saw α α α α α α

  22. Rutherford concluded • There had to be a heavy central core to the atom: the nucleus • Nucleus contains protons

  23. Nucleus • center of an atom • extremely small, positively charged, dense • contains protons, neutrons • surrounded by empty space where electrons move

  24. Proton • Subatomic particle • Exists in the nucleus • Has a positive charge (+1) • Has a mass of 1 atomic mass unit

  25. James Chadwick(1932) • Experimenting with radiation sources • Discovered a new particle with no charge : the neutron

  26. Neutron • subatomic particle • found in an atom’s nucleus • has a mass nearly equal to that of a proton (1 atomic mass unit) • Has a neutral charge (no charge)

  27. Nuclear Atomic Model • Neutrons (n0) • Protons (p+) • Electrons (e-) Workbook: Page 20, #5

  28. Electrons, Protons and Neutrons • Workbook: Page 20 • Numbers 5

  29. Structure of the atom • 99.97% of mass in nucleus • Most of the volume is empty space • Electrons in cloud

  30. How big is an atom? • Simulate the size of a hydrogen atom: • Nucleus : place a baseball on the 50 yard line of Reliant Stadium • Electron : put a grain of sand on the back row of the highest section

  31. Electrons, Protons and Neutrons • Workbook: Page 20 • Numbers 6, 7, 8

  32. Sub-subatomic particles • Protons, and neutrons are made of even smaller particles • 6 flavors of quarks • up, down, charm, strange, top, and bottom

  33. Differences in atoms • Different atoms - different numbers of protons and neutrons • The number of protons determines what the element is

  34. 6 C 12.0107 Wait… • Proton mass = 1 • Neutron mass = 1 • So where did those decimal places come from?

  35. 19 K 39.0983 Isotopes and atomic mass • Potassium has 19 protons • How many neutrons? 20 potassium atoms: 93.25% will have 20 neutrons, 6.7302% will have 22 neutrons, 0.0117% will have 21 neutrons

  36. Isotopes • Atoms of the same element with the same number of protons but different numbers of neutrons

  37. Video

  38. Atomic Number • The number of protons in an atom • Always a whole number • Number of electrons = number of protons Atomic number = protons = electrons

  39. 6 C 12.0107 Mass Number(whole number) • Total number of protons and neutrons in a given isotope Carbon-12 has 6 protons + 6 neutrons = 12 atomic mass units

  40. Carbon -12 is standard • Atomic Mass Unit (amu) is 1 / 12 the mass of a carbon – 12 atom • 1 amu is nearly (not exactly) equal to the mass of one proton or one neutron • Because of this, an atom’s mass is nearly equal to the number of protons and neutrons in its nucleus

  41. Isotopes • Atoms of the same element with the same number of protons but different numbers of neutrons

  42. 6 C 12.0107 Atomic Mass is an average(decimal) • An average of all known isotope mass numbers for an element • The atomic mass of an element is closest to the most common isotope found in nature • So, since Carbon’s atomic mass is closest to 12, carbon-12 would be the most common isotope found in nature

  43. Atoms review • Most atoms are neutral • Protons = electrons • Number of protons determines the element • Atomic number = number of protons

  44. Atoms on the periodic table

  45. Let’s Practice! • Complete 1-5 in study guide on page 21. • False • True • False (can be, but not always) • True • False

  46. More Practice! • Questions 6-12 on page 21. • 82 protons and 82 electrons • 8 protons • 30 • 85 • 104 protons and electrons • 84 protons and electrons • 102 protons and electrons

  47. Proton, neutron & electron relationships • Mass number = protons + neutrons • An isotope has an atomic number of 6 and a mass number of 13 • Number of protons, neutrons and electrons? Protons = 6 13 amu = 6 protons + _____ neutrons Electrons = 6 7

  48. Relationship Practice • On pages 21-22, questions 13-17. • Protons = 19, Electrons = 19, Neutrons = 20 • Protons = 14, Electrons = 14, Neutrons = 14 • Protons = 19, Electrons = 19, Neutrons = 21 • Protons = 51, Electrons = 51, Neutrons = 72 • 13 and 15 are both isotopes of Potassium

  49. There are two ways to represent elements: • Symbol: Mass Number =? _____________ Mass Number X # element symbol atomic # # (# of p+) Atomic Symbols # of p+ and n0 • Name: name of element followed by mass number. • Ex... Aluminum - 27 Atomic number =13 Nitrogen - 14 Atomic number =7 Atomic number =6 Carbon - 14 What are the Atomic Numbers for the above names?

  50. Symbol Name Nitrogen - 14 Nitrogen - 15 N N 14 15 7 7 For Example • There are two ways to represent nitrogen isotopes: