2. Atoms and their structure

3. History of the atom Original idea Ancient Greece (400 B.C..) Democritus Greek philosophers

4. History of Atom Looked at beach Made of sand n Smallest possible piece? n Atoms - not to be cut

5. Another Greek 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 His ideas were mostly opinion

6. Examples? Can you think of examples to prove invisible particles exist, even though we can’t see them?

7. Who Was Right? Greek society was slave based Beneath Famous to work with hands did not experiment Greeks settled disagreements by argument Aristotle was more famous He won His ideas carried through middle ages. Alchemists tried to change lead to gold

8. Who’s Next? 1808- John Dalton- England Teacher- summarized results of his experiments and those of other’s In Dalton’s Atomic Theory Combined ideas of elements with that of atoms

9. Dalton’s Atomic Theory 1. All matter is made of tiny indivisible particles (atoms) Dalton was wrong here 2. Atoms of the same element are identical 3. Atoms can’t be subdivided, created, or destroyed 4. Atoms of different elements combine in whole number ratios to form compounds 5. Chemical reactions involve the rearrangement of atoms.

10. Fundamental Laws of Chemistry Dalton used “atoms” to explain the following laws: 1. Law of Conservation of Mass Number of reactants = number of productsNumber of reactants = number of products 2. Law of Definite Proportions –Compounds have a constant composition by mass –Every sample of water is made up of 2 H and 1 O; NaCl = 1 Na and 1 Cl –Does not matter how many crystals of NaCl you have 3. Law of Multiple Proportions – If two elements make up more than one compound, then the ratio of the elements will always be a whole number ratio. –H 2 O and H 2 O 2 but not H 2.3 O 0.7

11. Analogy A bicycle has 2 wheels, a tricycle has three wheels. It’s a 2:3 ratio, a small, whole number ratio Now it’s your turn…

12. Laws of Multiple and Definete

13. Parts of Atoms J. J. Thomson - English physicist. 1897 Made a piece of equipment called a cathode ray tube. It is a vacuum tube - all the air has been pumped out, gas under low pressure Why? –Because without the pressure, the particles will flow easier

14. Thomson’s Experiment Voltage source + - Vacuum tube Metal Disks Anode Cathode

15. Thomson’s Experiment Voltage source +-

16. Thomson’s Experiment Voltage source +-

17. Thomson’s Experiment Voltage source +-

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

19. n Passing an electric current makes a ray appear to move from the negative to the positive end Thomson’s Experiment Voltage source +-

20. n Passing an electric current makes a ray appear to move from the negative to the positive end Thomson’s Experiment Voltage source +-

21. n Passing an electric current makes a ray appear to move from the negative to the positive end Thomson’s Experiment Voltage source +-

22. Thomson’s Experiment By adding an electric field

23. Voltage source Thomson’s Experiment n By adding an electric field + -

24. Voltage source Thomson’s Experiment n By adding an electric field + -

25. Voltage source Thomson’s Experiment n By adding an electric field + -

26. Voltage source Thomson’s Experiment n By adding an electric field + -

27. Voltage source Thomson’s Experiment n By adding an electric field + -

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

29. Thomson`s Model Found the electron Couldn’t find positive (for a while) Said the atom was like plum pudding Positive stuff, with the electrons randomly surrounding it Like watermelon, the seeds are spread throughout and do not contribute to the mass of the fruit

30. Millikan- 1909 Discovered the charge on the electron Gave it a unit- Coulomb (C) 1.602 x 10 -19 = q (q stands for charge) 1/2000 mass of hydrogen http://cwx.prenhall.com/petrucci/media lib/media_portfolio/02.html

31. Rutherford’s experiment Ernest Rutherford English physicist. (1910) Believed in the plum pudding model of the atom. Wanted to see how big they are Used radioactivity Alpha particles – He with pos. charge- given off by uranium Shot them at gold foil which can be made a few atoms thick

32. Lead block Uranium Gold Foil Florescent Screen

33. 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

34. What he expected

35. Because

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

37. What he got

38. How he explained it + Atom is mostly empty Small dense, positive pieceat center Alpha particles are deflected by it if they get close enough “It was like shooting a bullet at a piece of tissue paper and have the bullet reflect off the paper back at you”

39. +

40. What Did It Prove? The atom has a nucleus Small, dense bundle of positive charge Nucleus has a small volume compared to the rest of the atom

41. Niels Bohr 1913 suggested that electrons in an atom move in set paths around the nucleus Much like planets orbit around the sun

42. Summarize Create a table showing the experiment, date and discovery from each of the following: –Millikan, Dalton, Thomson, Rutherford

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

44. Subatomic particles Electron Proton Neutron NameSymbolCharge Relative mass Actual mass (g) e-e- p+p+ n0n0 +1 0 1/1840 1 1 9.11 x 10 -28 1.67 x 10 -24

45. Size of an atom Atoms are small. Protons and neutrons = nucleus Nucleus tiny compared to atom If the atom was the size of a stadium, the nucleus would be the size of a marble. Radius of the nucleus near 10 -15 m. Density near 10 14 g/cm What charge does the nucleus contain?

46. Flinn Mapping the Atom activity

47. Questions Three compounds containing O and k have 1.22g, 2.44g and 4.89g of K. Show how this data supports the L.M.P. Compare in terms of location, mass and charge- electrons, proton and neutron If I change the number of protons in a substance, will it be the same substance?

48. Counting the Pieces Atomic Number = number of protons # of protons determines kind of atom Same as the number of electrons in the neutral atom Atomic Mass = the number of protons + neutrons (AKA Mass Number) –All the things with mass

49. Symbols Contain the symbol of the element, the mass number and the atomic number X Mass number Atomic number

50. Symbols Find the –number of protons –number of neutrons –number of electrons –Atomic number –Mass Number F 19 9

51. Symbols n Find n Find the –number –number of protons of neutrons of electrons –Atomic –Atomic number –Mass –Mass Number Br 80 35

52. Symbols n if an element has 91 protons and 140 neutrons what is the –Atomic number –Mass number –number of electrons –Complete symbol

53. Ions Atoms that have a different number of electrons than they should have –Gives the atom a charge –Example: Carbon should have 6 electrons, but C + has 5 electrons. What charge does it have?

54. Isotopes Dalton was wrong again Atoms of the same element can have different numbers of neutrons –different mass numbers –called isotopes Example: Carbon-12; Carbon-13 –Both have 6 protons –Carbon-12 has a relative mass of 12, Carbon-13 has a relative mass of 13 What’s Carbon-14?

55. Naming and Writing Isotopes Put the mass number after the name of the element carbon- 12 carbon -14 uranium-235 To write them, Put protons on bottom and mass number on top: C 14 7

56. Question How many p, e and n are in an atom of Cl- 37? Mass number – atomic number = neutrons 37-17 = 20 17 p, 17 e, 20 n Practice- Pg 80

57. Measuring Atomic Mass Unit is the Atomic Mass Unit (amu) One twelfth the mass of a carbon-12 atom. Each isotope has its own atomic mass we need the average from percent abundance. Can a single atom have an AMU?

58. Atomic Mass Is not a whole number because it is an average. –The decimal numbers are on the periodic table It’s like calculating your grade- it’s made of percentages that are weighted

59. Average Atomic Mass How heavy is an atom of oxygen? –There are different kinds of oxygen atoms. = abundance of each element in nature. Average of all the types of one element Don’t use grams because the numbers would be too small

60. Calculating averages You have five rocks, four with a mass of 50 g, and one with a mass of 60 g. What is the average mass of the rocks? Total mass = 4 x 50 + 1 x 60 = 260 g Average mass = 4 x 50 + 1 x 60 = 260 g 5 5 Average mass = 4 x 50 + 1 x 60 = 260 g 55 5

61. Calculating averages Average mass = 4 x 50 + 1 x 60 = 260 g 5 5 Average mass =.8 x 50 +.2 x 60 80% of the rocks were 50 grams 20% of the rocks were 60 grams Average = % as decimal x mass + % as decimal x mass + % as decimal x mass +

62. Atomic Mass Calculate the atomic mass of copper if copper has two isotopes. 69.1% has a mass of 62.93 amu and the rest has a mass of 64.93 amu. (62.93*.691) + (64.93*?) = Answer(62.93*.691) + (64.93*?) = Answer How do you find ??How do you find ?? 100-69.1 = 30.9% 100-69.1 = 30.9% (62.93*.691) + (64.93*.309) = 63.548(62.93*.691) + (64.93*.309) = 63.548 Check:Check: Periodic table Periodic table Sig Figs Sig Figs Label Label

63. Atomic Mass Magnesium has three isotopes. 78.99% magnesium-24 with a mass of 23.9850 amu, 10.00% magnesium-25 with a mass of 24.9858 amu, and the rest magnesium-25 with a mass of 25.9826 amu. What is the atomic mass of magnesium?

64. Moles and Mass One mole of an element is equal to it’s mass AMU Avegadro’s number is the number of particles in one mole of that substance Example- You have one mole of Pt, what is it’s AMU? Example- A mass of 2 g of Be contains how many moles?

65. Review How many p, e, n make up at atom of carbon-13? Write the symbol for oxygen-16 What’s the difference between isotope and ion? Create an pneumonic device for this difference.

66. Science Humor A neutron walks into a bar. "I'd like a soda" he says. The bartender promptly serves up a soda. "How much will that be?" asks the neutron. "For you?" replies the bartender, "no charge" Q: What happens when electrons lose their energy? A: They get Bohr'ed. Q: What did the thermometer say to the graduated cylinder? A: "You may have graduated but I've got many degrees" A hydrogen atom came running into a police station asking for help.... Hydrogen atom: "Someone just stole my electron!" Policeman: "Are you sure?" Hydrogen atom: "Yes, I'm positive" Policeman: "Oh, I thought you were just being negative again."