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Chapter 5

Chapter 5. Atomic Structure. EARLY MODLES OF THE ATOM. 5 th Century B.C. Greek Philosopher – Democritus thought up the idea that all matter was made of tiny, indivisible particles He called them Atomos which means indivisible Other philosophers didn’t believe him. Another Greek Thinker.

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Chapter 5

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  1. Chapter 5 Atomic Structure

  2. EARLY MODLES OF THE ATOM • 5th Century B.C. • Greek Philosopher – Democritus thought up the idea that all matter was made of tiny, indivisible particles • He called them Atomos which means indivisible • Other philosophers didn’t believe him

  3. Another Greek Thinker • Aristotle - Famous philosopher • All substances are made of 4 elements • Fire - hot • Air - light • Earth - cool, heavy • Water - wet • Blend these in different proportions to get all substances

  4. Who Was Right? • They did not experiment – they didn’t have the instruments to do that • These Greeks settled disagreements by argument. • Aristotle was a better debater - He won. • His ideas carried through middle ages.

  5. Who’s Next? • Late 1700’s - John Dalton- England. • Teacher- summarized results of his experiments and those of others. • Elements are substances that can’t be broken down • Came up with his own theory

  6. Dalton’s Atomic Theory • All matter is made of tiny indivisible particles called atoms. • Atoms of the same element are identical, those of different atoms are different. • Atoms of different elements combine chemically in whole number ratios to form compounds. • Chemical reactions involve the rearrangement of atoms. No new atoms are created or destroyed.

  7. WHAT DOES THAT MEAN????? • 1. 1st part TRUE b/c Atoms are the smallest piece of an element that keeps the characteristics of that element 2nd part FALSE b/c atoms can be broken down into smaller pieces (ex: protons, neutrons, electrons) • 2. 1st part FALSE b/c of discovery of ions and isotopes for atoms of the same element (Ex: Carbon-12 vs. Carbon-14 and H+ vs. H); 2nd part TRUE • 3. TRUE - A compound has to have the same ratio of elements to be considered that particular compound – Ex H2O or H2O2two different ratios mean, two different compounds • 4. TRUE b/c of Law of _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

  8. What did Dalton think this atom looked like? • Picture a tiny billiard ball • It is dense and is a solid object.

  9. Size of an atom • Atoms are small. • IF an atom was the size of a stadium, like Rentschler Field, the nucleus would be the size of a marble on the 50 yard line.

  10. How were the different parts of the atom found?

  11. Parts of Atoms • J. J. Thomson - English physicist -1897 • Made a piece of equipment called a cathode ray tube.

  12. Voltage source Thomson’s Experiment - + Metal Disks

  13. Voltage source Thomson’s Experiment - + • Passing an electric current makes a beam appear to move from the negative to the positive end

  14. Voltage source Thomson’s Experiment + - • By adding an electric field

  15. Voltage source Thomson’s Experiment + - • By adding an electric field he found that the moving pieces were negative • By adding an electric field

  16. Thomson’s Experiment • Did many different experiments with gases inside the tube. • Found that the cathode rays were attracted to positively charged electric plates • Decided that the rays were made up of tiny particles moving at high speeds

  17. Thomson’s Model • Found the electron. • Said the atom was like plum pudding. • A bunch of positive stuff, with the electrons stuck in it. But the electrons could be removed.

  18. Atomizer + - Oil Microscope Metal Plates Millikan’s Experiment

  19. Atomizer Oil droplets + - Oil Microscope Millikan’s Experiment

  20. Millikan’s Experiment X-rays X-rays give some drops a charge by knocking offelectrons

  21. + - Millikan’s Experiment

  22. Millikan’s Experiment - - + + They put an electric charge on the plates

  23. Millikan’s Experiment - - + + Some drops would hover

  24. + Millikan’s Experiment - - - - - - - Some drops would hover + + + + + + +

  25. Millikan’s Experiment - - + + From the mass of the drop and the charge on the plates, he calculated the charge on an electron

  26. Rutherford’s Experiment • Ernest Rutherford English physicist. (1910) • Believed the plum pudding model of the atom was correct. • Wanted to see how big they are. • Used radioactivity. • Alpha particles - positively charged pieces given off by uranium. • Shot them at gold foil which can be made a few atoms thick.

  27. Rutherford’s experiment • When the alpha particles hit a florescent screen, it glows. • Here’s what it looked like (pg 72)

  28. Flourescent Screen Lead block Uranium Gold Foil

  29. He Expected • The alpha particles to pass through without changing direction very much. • Because… • The positive charges were spread out evenly. Alone they were not enough to stop the alpha particles.

  30. What he expected

  31. Because

  32. Because, he thought the mass was evenly distributed in the atom

  33. Because, he thought the mass was evenly distributed in the atom

  34. What he got

  35. + Rutherford’s Model • Atom is mostly empty. • Small dense, positive piece at center – called the nucleus

  36. +

  37. Modern View • The atom is mostly empty space. • Two regions. • Nucleus- protons and neutrons. • Electron cloud- region where you might find an electron.

  38. Density and the Atom • Since most of the particles went through, it was mostly empty. • Because the pieces turned so much, the positive pieces were heavy. • Small volume, big mass, big density. • This small dense positive area is the nucleus. • Radius of the nucleus is near 10-15m. • Density near 1014 g/cm3.

  39. Other pieces • Proton - positively charged pieces has a lot of mass • Neutron - no charge but the same mass as a proton. • Electron – negatively charged, very light it takes 1840 of them to equal the mass of a proton or neutron

  40. Subatomic particles Relative mass Location Name Symbol Charge Electron e- -1 0 amu Electron Cloud 1 amu Proton p+ +1 nucleus Neutron n0 0 nucleus 1 amu

  41. Counting the Pieces • Atomic Number = number of protons • # of protons determines kind of atom. • the same as the number of electrons in the neutral atom. • Mass Number = the number of protons + neutrons. • All the things with mass. • NOT on the periodic table

  42. Isotopes & Ions • ISOTOPES • Atoms of the same element can have different numbers of neutrons. • different mass numbers. • IONS • Atoms of the same element with different numbers of electrons • Different charges • Ion with more protons than electrons has a positive charge • Ion with more electrons than protons has a negative charge

  43. Symbols • Contain the symbol of the element, the mass number, the atomic number and the charge

  44. Symbols • Contain the symbol of the element, the mass number and the atomic number. Mass number Charge X Atomic number

  45. Naming Isotopes • Put the mass number after the name of the element. • carbon- 12 • carbon -14 • uranium-235

  46. Symbols • Find the • number of protons • number of neutrons • number of electrons • Atomic number • Mass Number • Name 24 Na 11

  47. Symbols • Find the • number of protons • number of neutrons • number of electrons • Atomic number • Mass Number • Name 80 - Br 35

  48. Symbols • If an element has an atomic number of 30 and a mass number of 64 what is the • number of protons • number of neutrons • number of electrons • Complete symbol • Name

  49. Symbols • if an element has 92 protons and 144 neutrons what is the • Atomic number • Mass number • number of electrons • Complete symbol • Name

  50. Symbols • If an element has 82 protons, 80 electrons and 117 neutrons what is the • Atomic number • Mass number • number of protons • Complete symbol • Name

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