Professor Robert Hazen UNIV 301 KEY IDEA: Properties of

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Great Ideas in ScienceLecture 6 Properties of
Materials

• Professor Robert Hazen
• UNIV 301

KEY IDEA Properties of materials depend on their
atoms, and how those atoms are linked together
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Tonights Outline

• Review Chemical Bonding
• Chemical Reactions
• Properties of Materials
• States of matter
• Changes of state
• Strength of materials
• Magnetic properties
• Electrical properties

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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

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Ionic Bonding
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Ionic Bonding
Ionic Bonding
Na
Cl
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Ionic Bonding
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Ionic Bonding
Mg 2Cl
MgCl2
Mg 2Cl
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Ionic Bonding
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Metallic Bonding
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Metallic Bonding
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Covalent Bonding
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Covalent Bonding
Hydrogen
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Covalent Bonding
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Covalent Bonding
WATER
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Covalent Bonding
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Covalent Bonding Carbon
CARBON BONDING Organic Chemistry
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Covalent Bonding Carbon
CARBON BONDING Organic Chemistry
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States of Matter
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SOLIDS(fixed volume and shape)

• Crystal regular atomic arrangement

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SOLIDS(fixed volume and shape)
Glass Atoms not periodic
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Glass vs. Crystal Structure
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Solids Plastics
Plastics Formed from chains of molecules
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Plastic Recycling
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LIQUIDS (fixed volume, variable shape)
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LIQUIDS (fixed volume, variable shape)
Liquid Crystals Molecules line up under an
electric field
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GAS (variable volume and shape)
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PLASMA (Gas with free electrons)
By far the most abundant state of matter in
the universe!!!
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Changes of State
HYDROCARBONS
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Distillation (Fractionation) Column

• Gasoline, kerosene, diesel fuel, asphalt tar
  are distilled from crude oil.

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Chemical Reactions Oxidation Reduction
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Chemical Reactions Oxidation Reduction
Rusting Oxidation
Smelting Reduction
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Chemical ReactionsAcid Base Reactions
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Chemical Reactions Polymerizaton
Depolymerization

• Addition Polymerization

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Chemical Reactions Polymerizaton
Depolymerization

• Condensation Polymerization

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Materials and the Modern World

• Materials define a societys technical
  sophistication
• Chemists contributions
• Properties of Materials
• The kind of atoms of which it is made
• Arrangement of atoms
• Type of bonding of atoms

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Different Kinds of Strength

• Strength
• Compressive
• Tensile
• Shear
• Elastic Limit
• Strength depends on the types and arrangements of
  bonds

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Compressive Strength(Strength against
squeezing)

• Stack of paper
• Masonry
• Wood

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Tensile Strength(Strength against pulling)

• Wire
• Rope
• Chains

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Shear Strength(Strength against twisting)

• Girder network
• Diamond

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Composite Materials

• Combination of materials increases strength
• Reinforced concrete
• Plywood
• Fiberglass

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Magnetic Properties of Materials

• Magnetic field
• Due to electrical current
• Electrons spinning
• Arrangement of atomic magnets
• Degree of alignment determines the strength of
  magnetism

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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

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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.

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Semiconductors

• Semiconductors neither good conductors nor
  insulators
• Example Silicon

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Semiconductors Phosphorus doped
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n-type Semiconductors

• Dope with phosphorus
• One extra electron for each P

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Semiconductors Aluminum doped
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p-type Semiconductors

• Dope with aluminum
• A missing electron hole

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p-type Semiconductors

• Dope with aluminum
• A missing electron hole

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Diodes

• A junction of p- and n-type semiconductors
• creates a one-way valve

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The Transistor

• Transistor
• Control flow of electrons
• Emitter
• Base
• Collector
• Uses
• Cell phone
• Computer

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The Transistor as an Amplifier
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Microchips (Integrated Circuits)

• Complex array of p- and n-type semiconductors
• Designed with layers interconnected

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Microchips and the Information Revolution

• New materials often lead to new technologies that
  change society

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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

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Two Developing Technologies

• Computers store and manipulate information
• Nanotechnology the future of materials science