1. Lecture 5 –The Atom
Great Idea: “All matter is made of atoms, which have a positively-charged nucleus surrounded by negatively-charged electrons.”

2. Electricity and magnetism are two aspects of the same force.
All magnets have both north
and south poles
Static electricity is manifest as a force between charged objects
Electricity produces magnetic effects.
Moving magnets produce electricity.

3. The Electrical Field
The force felt by a charge located at a particular point
Differs from the magnetic dipole field

4. Magnetic Effects from Electricity

5. North and South poles flip during rotary motion.
The Electric Motor
North and South poles flip during rotary motion.

6. Review – Maxwell’s Equations for Electricity & Magnetism
Coulomb’s law of static electricity
All magnets have both North and South poles
Electricity produces magnetic fields
Moving magnets produce electricity:

7. Maxwell’s Laws, 1855 These equations lead to prediction of waves:
1. Waves travel 186,000 miles per second
2. Light is a consequence of electricity and
magnetism switching back and forth

8. Review – Maxwell’s Equations for Electricity & Magnetism
Maxwell’s prediction of many kinds of electromagnetic radiation

9. Energy Transfer by Waves
Carry energy
Matter doesn’t move
Properties of Waves
Wavelength
Frequency
Velocity
Amplitude

10. The Relationship Among Wavelength, Frequency, and Velocity
velocity of a wave = wavelength x frequency

11. Properties of Electromagnetic Waves
Wavelength (e.g. crest to crest) – Any value
Frequency (number per second) – Any value
Speed = 300,000 kilometers per second
= 186,000 miles per second
Amplitude (height of the wave)

12. Electromagnetic Spectrum
Diagram of EM spectrum (w/ color)

13. Properties of Electromagnetic Waves
Relationship between short & long waves
Short waves = high frequency = high energy
Long waves = low frequency = low energy
Matter interacts with light in 3 ways:
Transparent – light passes through
Absorbing – matter soaks up energy
Scattering – light bounces off

14. Some Matter is Transparent to Light
Light waves pass through
transparent materials

15. Some Matter Absorbs Light
Light waves are absorbed:
Materials soak up energy

16. Some Matter Scatters Light
Light waves hit and
bounce off in many directions

17. Scattering (Reflection)

18. Scattering (Refraction)

19. Electromagnetic Spectrum
Diagram of EM spectrum (w/ color)

20. Radio waves Produced when electrons accelerate
Amplitude increases with amplifier power
Most everyday objects are
transparent to radio waves
Walls, ceiling, windows, doors
Metals absorb radio waves
That’s why antennas are made of metal
What scatters radio waves?
Ionosphere, especially at night

21. Radio Telescope

22. Amplitude Modulation (AM)
Carrier waves
Modulated signal by altering amplitude
Analogous to turning a flashlight off and on

23. Frequency Modulation (FM)
Carrier waves
Modulated signal by altering frequency
Analogous to switching a flashlight from yellow to blue

24. Electromagnetic Spectrum
Diagram of EM spectrum (w/ color)

25. Microwaves
3 major uses in our society
Cooking (Ovens)

26. Microwaves 3 major uses in our society
Cell phones (point-to-point communications)

27. Microwaves
3 major uses in our society
Radar (stealth technology)

28. Electromagnetic Spectrum
Diagram of EM spectrum (w/ color)

29. Infrared Radiation (Heat)

30. Infrared Radiation (Heat)

31. Electromagnetic Spectrum
Diagram of EM spectrum (w/ color)

32. Visible Light

33. Visible Light

34. Electromagnetic Spectrum
Diagram of EM spectrum (w/ color)

35. Higher Energy Spectra (Potential Cell Damage)
High energy = short wavelengths
Ultraviolet radiation
Sunblock

36. Higher Energy Spectra (Potential Cell Damage)
High energy = short wavelengths
X-Rays
Medicine

37. Material Properties [NEXT WEEK]
Atoms alone
Structure
Periodic Table
Chemical Bonding
Types of bonds
Chemical Reactions
Material Properties [NEXT WEEK]
States of matter
Mechanical & Electrical Properties

38. The atom
GREAT IDEA: All matter is made of atoms which have a positively-charged nucleus surrounded by negatively-charged electrons.
KEY WORDS:
Atom
Proton
Neutron
Electron
Atomic Number
Nucleus
Ion
Periodic Table of Elements

39. Are Atoms Real?

40. Evidence for Atoms
1. Behavior of gas
2. Ratios of elements

41. Evidence for Atoms 1. Behavior of gas 2. Ratios of elements
3. Radioactivity
4. Brownian Motion – Einstein

42. Evidence for Atoms 5. Avogadro's number (6.0221415 x 1023)
6. X-ray diffraction
7. Atomic microscopy

43. Is there something smaller?
Electron (J. J. Thompson)

44. Is there something smaller?
Electron (J. J. Thompson)
Negatively charged
Easily stripped off atoms
Mass is negligible

45. Is there something smaller?
Rutherford Scintillation Experiments

46. Is there something smaller?
Rutherford Scintillation Experiments
Atomic “bullets” hit gold foil
A few bounce backwards
Reveals tiny but massive atomic nucleus

47. Niels Bohr’s Model of the Atom

48. Niels Bohr’s Model of the Atom
Electrons occur in fixed energy levels (shells)

49. Electron energy levels are analogous to standing waves
Bohr Model of the Atom
Electron energy levels are
analogous to standing waves

50. Changes levels = Quantum leaps Photon = single light wave emitted
Bohr Model of the Atom
Changes levels = Quantum leaps
Photon = single light wave emitted

51. Properties of Electromagnetic Waves
Matter and light interact in three ways:
Matter can be transparent to light.
Matter can absorb light.
Matter can scatter light.

52. Quantum Mechanics
At the scale of atoms, everything comes in “quanta” (bundles).
You can’t measure a property without changing the object being measured.
Every measurement requires:
A sample,
A source of energy,
A detector.

53. Absorption of Light

54. Is There Any Order to the Different Kinds of Atoms?
Dimitri Mendeleev
ca. 1867

55. Periodic Table of the Elements

56. Periodic Table of the Elements

57. Chemical Bonding
Key Idea: Atoms link together by the rearrangement of their electrons
1. “Magic” numbers of electrons (i.e. 2, 10, 18 and 36) form very stable atoms.
2. Electrons may be transferred or shared to form stable bond
3. Ionic, metallic and covalent bonds

58. Periodic Table of the Elements

59. Ionic Bonding

60. Periodic Table of the Elements

61. Metallic Bonding

62. Periodic Table of the Elements

63. Covalent Bonding
Hydrogen

64. Periodic Table of the Elements

65. Covalent Bonding
WATER