1. DOR Chemical/Physical Changes  Classify each change as either chemical or physical. 1) Gasoline in your engine burns as you start the car. 2) Distilled water 3) Rust on a nail 4) Glow sticks 5) Medicine crushed into a powder

2. The Atom

3. Law of Conservation of Mass/Matter  Matter cannot be created or destroyed  Total mass is constant in chemical reactions.  Originated with Antoine Lavoister (1700s)  Quantitative mass data of reactants and products in mercury oxide decomposition.

4. Law of Definite Proportions  Proposed by Joseph Proust (late 1700s)  Decompositions and research with copper carbonate  Compound composition and properties are fixed  All compound samples have the same composition  Same % of elements in the compound  Ex. H 2 O

5. Law of Multiple Proportions  2+ compounds with same 2 elements, one element masses combined with second element’s mass in whole number ratio.  Compositions of these compounds are related  Proposed by John Dalton in addition to his atomic theory.  Ex. CO 2 (2:1), CO (1:1)

6. Terminology  Element– basic unit of a substance, contain only ONE type of atom, represented by symbol. Example: Ag, only contains Ag atoms.  Atom—smallest particle of an element that still contains element properties.  Example: One atom of Au, cannot have a smaller particle of gold and still be gold.

7. Compound vs. Molecule  Compounds:  more than one element  elements combined in definite proportions  Molecule:  Smallest unit of a compound that still retains the properties of the compound.

8. How far back does the “atom” go?  Democritus  400 B.C.  Called the basic unit of matter an “atom”

9. The Atom and its Structure

10. Dalton Atomic Theory  1800s  Atoms make up elements.  Atoms form compounds as a whole and cannot be divided. Compounds formed from atoms joining in FIXED proportions

11. Dalton Atomic Theory (cont.)  All matter made of atoms  Atoms of an element have the same size, mass, etc.  Different atoms have various sizes, mass, etc.  Atoms cannot be divided, destroyed, or created.  Atoms rearrange in chemical reactions.

12. John Thomson  1897  Cathode-Ray experiments.  Discovered the electron particle and its possible charge.  Stated electrons have a negative charge  Determined ratio between mass and charge of an electron

13. Robert Millikan Robert Millikan  1909, American  Found the mass of an electron (VERY small) with Thompson’s data  Currently, mass of electron = 9.109 x 10 -31 kg  Discovered electron charge  e = -1.602 x 10 -19 C  Oil drop experiments.

15. Early Models of the Atom Thompson  Must be a balance between negative and positive charges  “Raisin-Pudding” model  Uniform distribution of positive charge  Positive cloud with stationary electrons

17. Early Models of the Atom Rutherford  How are electrons distributed in an atom?  Discovered alpha particles as 4 2 He  Experiments with Au, Ag, and Pt foils bombarded with alpha particles

19. Early Models of the Atom Rutherford  Mostly empty space  Small, positive nucleus  Contained protons  Negative electrons scattered around the outside

20. James Chadwick  SOOO we have protons and electrons…anything else?  Experiments shooting alpha particles at Beryllium atoms  Colleague of Rutherford  Participated in Manhattan Project  1932 discovered neutrons contained in atom’s nucleus  No charge  Mass approximately same as proton mass

21. Early Models of the Atom Bohr  1913—hydrogen atom structure  Physics + quantum theory  Electrons move in definite orbits around the positively charged nucleus— planetary model  Does not apply as atoms increase in electron number

22. Erwin Schrödinger  Quantum mechanics  1926---wave equation  Electrons behave more like waves than particles

23. Heisenberg’s Uncertainty Principle  Electron’s location and direction cannot be known simultaneously  Electron as cloud of negative charge

24. Modern Model of the Atom The electron cloud  Sometimes called the wave model  Electron as cloud of negative charge  Spherical cloud of varying density  Varying density shows where an electron is more or less likely to be

25. Homework  Read pp. 36-39, 263-267, 276-280

26. DOR: Atomic Theory 9/4 1) Which scientist is credited with the Law of Conservation of Mass? 2) This scientist performed cathode ray experiments to determine the ratio between the mass and charge of an electron. 3) This scientist found the actual mass and charge of an electron following up on another scientist’s data. 4) An electron’s location and direction cannot be simultaneously known. This statements is from _______________________________________

27. How did we discover electron arrangement in an atom? ELECTROMAGNETIC RADIATION ! ! !

28. Waves  Repeated disturbance through a medium (air, liquid) from origin to distant points.  Medium does not move  Ex. Ocean waves, sound waves

29. Characteristics of Waves  Wavelength  Distance between 2 points within a wave cycle  2 peaks  Frequency  # of wave cycles passing a point for a particular time unit  Usually seconds.

31. Wavelength and frequency are inversely proportional.

32. c = νλ c = νλ c = speed of light, 3.0 x 10 8 m/s ν= frequency (s -1 ) λ= wavelength (nm)

33. Electromagnetic Waves  Produced from electric charge movement  Changes within electric and magnetic fields carried over a distance  No medium needed

34. Electromagnetic Spectrum  Contains full range of wavelengths and frequencies found with electromagnetic radiation  Mostly invisible, visible range (390 nnm -760 nm)  Different materials absorb/transmit the spectrum differently.

36. Types of Spectra  What is a spectra?  Spectrum– white light/radiation split into different wavelengths and frequencies by a prism  Continuous spectrum  No breaks in spectrum  Colors together  Line spectrum  Line pattern emitted by light from excited atoms of a particular element  Aided in determining atomic structure

37. Line Spectrum  Pattern emitted by light from excited atoms of an element  Specific for each element  Used for element identification

41. Flame Tests  Some atoms of elements produce visible light if heated  Each element has a specific flame color  Examples: Li, Na, Cs, Ca

42. A Bit of Quantum Theory……

43. Max Planck  1900  Related energy and radiation  E = hν  h= 6.626 x 10 -34 J  s (Planck’s constant)  Quantum ---smallest amount of energy  Atoms can only absorb/emit specific quanta

44. Albert Einstein  1905  Added to Planck’s concept  Photons—  Bundles of light energy  Same energy as quantum  E = hν (energy of photon)  Photons release energy and electrons gain energy  Threshold frequency– minimum amount of energy needed by photon to extract electron

45. THEREFORE ………  Light is in the form of electromagnetic waves  Photons can resemble particles  Gave raise to the possibility of thinking about wave AND particle qualities of subatomic particles (electron)

46. Example 1 Calculate the energy found in a photon of red light with a wavelength of 700.0 nm

47. Example 2 How much energy (in joules) is found in the radiation of the hydrogen atom emission spectrum with a 656.3 nm wavelength?

48. Homework 9/4/13  Read over Law of Conservation of Mass lab procedure.  Read pp. 267-274  Problems p. 293 #31  Problems p. 294 #37, 38, 41, 42

49. DOR: Test Survey 1) How much time did you spend outside of class in preparation for Test I ? 1) What materials did you use to study for the test? 1) Was the test material represented through the study guide and class materials? 1) What grade do you feel you deserve on the test?

50. Atomic Structure  Nucleus  Protons  Neutrons  Electrons

51. Atomic Structure  Electrons  Tiny, very light particles  Have a negative electrical charge (-)  Move around the outside of the nucleus

52. Atomic Structure  Protons  Much larger and heavier than electrons  Protons have a positive charge (+)  Located in the nucleus of the atom  Located in the nucleus of the atom

53. Atomic Structure  Neutrons  Large and heavy like protons  Neutrons have no electrical charge  Located in the nucleus of the atom  Located in the nucleus of the atom

54. Atomic Structure

55. Describing Atoms  Atomic Number = number of protons  In a neutral atom, the # of protons = the # of electrons  Atomic Mass= the number of protons + the number of neutrons

56. Isotopes  The number of protons for a given atom never changes.  The number of neutrons can change.  The number of neutrons can change.  Two atoms with different numbers of neutrons are called isotopes  Isotopes have the same atomic #  Isotopes have different atomic Mass # ’ s

57. Isotopes

58. Ions  An atom that carries an electrical charge is called an ion  If the atom loses electrons, the atom becomes positively charged.  If the atom gains electrons, the atom becomes negatively charged

59. Ions  The number of protons does not change in an ion.  The number of neutrons does not change in an ion.  So, both the atomic number and the atomic mass remain the same.

60. Ex. 1: Ca

61. Ex. 2: H +1

62. Ex. 3: Bi-212

63. PEN Method for---  O -2 P  F S -2  Li +1 Cl  Ba +2 Na  MgPo-215  C -14Al +3  NRa-226  U-235U-238