1. Great Ideas in Science: Lecture 6 – Properties of Materials
Professor Robert Hazen
PROV 301
KEY IDEA: Properties of materials depend on their atoms, and how those atoms are linked together

2. Tonight’s Outline Review Chemical Bonding Chemical Reactions
Properties of Materials
States of matter
Changes of state
Strength of materials
Electrical properties

3. 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 bonds.
3. Ionic, metallic, and covalent bonds

4. Ionic Bonding

5. Ionic Bonding
Ionic Bonding Na Cl

6. Ionic Bonding

7. Ionic Bonding

8. Ionic Bonding
Mg + 2Cl
MgCl2
Mg + 2Cl

9. Ionic Bonding
Fluorite CaF2

10. Ionic Bonding
Two properties of materials with ionic bonds: 1. Insulates electricity—“insulator” (electrons don’t move) 2. Tough but brittle—cup demo.

11. Metallic Bonding

12. Metallic Bonding

13. Metallic Bonding

14. Metallic Bonding
Three properties of materials With metallic bonds: 1. Conducts electricity—Wire (electrons free to move) 2. Malleable—Coat hanger 3. Shiny

15. Covalent Bonding

16. Covalent Bonding
Hydrogen

17. Covalent Bonding

18. Covalent Bonding
WATER

19. Covalent Bonding

20. Covalent Bonding: Carbon4 2 C 3 1
(R)-enantiomer
CARBON BONDING
Organic Chemistry

25. Covalent Bonding: Carbon4 2 C 3 1
(R)-enantiomer
CARBON BONDING
Organic Chemistry

26. States of Matter

27. SOLIDS (fixed volume and shape)
Crystal – regular atomic arrangement

28. SOLIDS (fixed volume and shape)
Glass: Atoms not periodic

29. Glass vs. Crystal Structure

30. Solids: Plastics
Plastics: Formed from chains of molecules

31. Plastic Recycling

32. LIQUIDS (fixed volume, variable shape)

33. LIQUIDS (fixed volume, variable shape)
Liquid Crystals: Molecules line up under an electric field

34. GAS (variable volume and shape)

35. PLASMA (Gas with free electrons)
By far the most abundant state of matter in the universe!!!

36. Changes of State
HYDROCARBONS

37. Changes of State
Gas
Liquid
Solid
How does a candle work?

38. Distillation (Fractionation) Column
Gasoline, kerosene, diesel fuel, asphalt & tar are distilled from crude oil.

39. Chemical Reactions: Oxidation & Reduction

40. Chemical Reactions: Oxidation & Reduction
Rusting = Oxidation
Smelting = Reduction

41. Chemical Reactions: Acid & Base Reactions

42. Chemical Reactions: Acid & Base Reactions

43. Chemical Reactions: Polymerizaton & Depolymerization
Addition Polymerization

44. Chemical Reactions: Polymerizaton & Depolymerization
Condensation Polymerization

45. Materials and the Modern World
Materials define a society’s technical sophistication
Chemists’ contributions
Properties of materials result from:
The kind of atoms of which it is made
The arrangement of those atoms
Type of bonding between those atoms

46. Different Kinds of Strength
Compressive
Tensile
Shear
Elastic Limit = the breaking point
Strength depends on the types and arrangements of bonds

47. Compressive Strength: (Strength against squeezing)
Stack of paper
Masonry
Wood

48. Tensile Strength: (Strength against pulling)
Wire
Rope
Chains

49. Shear Strength: (Strength against twisting)
Girder network
Diamond

50. Composite Materials Combination of materials increases strength
Reinforced concrete
Fiberglass
Plywood

51. Modern electronics control the flow of electrons
Key Idea
Modern electronics control the flow of electrons
Metals are conductors of electricity, while ionic and covalently-bonded materials are electrical insulators
Semiconductors conduct electricity under carefully controlled conditions
Key Words
p-type and n-type
diode
integrated circuit
microchip

52. Conductors & Insulators
Electrical conductors allow electrons to flow freely.
Electrical resistors drain some energy from an electrical current.
Electrical insulators prevent the flow of electricity.

53. Semiconductors Semiconductors: neither good conductors nor insulators
Example: Silicon

54. Semiconductors: Silicon

55. Semiconductors: Phosphorus doped

56. n-type Semiconductors
Dope with phosphorus
One extra electron for each P

57. Semiconductors: Aluminum doped

58. p-type Semiconductors
Dope with aluminum
A missing electron = hole

59. p-type Semiconductors
Dope with aluminum
A missing electron = hole

60. A junction of p- and n-type semiconductors creates a one-way valve
Diodes
A junction of p- and n-type semiconductors
creates a one-way valve

61. The Transistor Transistor Uses Control flow of electrons Cell phone
Emitter
Base
Collector
Uses
Cell phone
Computer

62. The Transistor as an Amplifier

63. Microchips (Integrated Circuits)
Complex array of p- and n-type semiconductors
Designed with many interconnected domains

64. Microchips and the Information Revolution
New materials often lead to new technologies that change society

65. Information The binary digit or bit
Two possible answers to a simple question
8 bits = 1 byte
All information can be reduced to bits
Visual information can be reduced to pixels

66. Two Developing Technologies
Computers store and manipulate information
Nanotechnology – the future of materials science