Transcript Great Ideas in Science: Lecture 6 – Chemical

Professor Robert Hazen
UNIV 301
KEY IDEA: Properties of
materials depend on their
atoms, and how those
atoms are linked together
Tonight’s Outline
 Review Chemical
Bonding
 Chemical Reactions
 Properties of Materials
 States of matter
 Changes of state
 Strength of materials
 Magnetic properties
 Electrical properties
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
Ionic Bonding
Ionic Bonding
Ionic Bonding
Na
Cl
Ionic Bonding
Ionic Bonding
Mg + 2Cl
Mg + 2Cl
MgCl
2
Ionic Bonding
Metallic Bonding
Metallic Bonding
Covalent Bonding
Covalent Bonding
Hydrogen
Covalent Bonding
Covalent Bonding
WATER
Covalent Bonding
Covalent Bonding: Carbon
1
C CARBON BONDING
Organic2Chemistry
4
3
(R)-enantiomer
Covalent Bonding: Carbon
1
CARBON BONDING
Organic Chemistry
C
4
2
3
(R)-enantiomer
States of Matter
SOLIDS
(fixed volume and shape)
Crystal – regular atomic arrangement
SOLIDS
(fixed volume and shape)
Glass: Atoms not periodic
Glass vs. Crystal Structure
Solids: Plastics
Plastics: Formed from chains of molecules
Plastic Recycling
LIQUIDS
(fixed volume, variable shape)
LIQUIDS
(fixed volume, variable shape)
Liquid Crystals: Molecules line up under an electric field
GAS
(variable volume and shape)
PLASMA
(Gas with free electrons)
By far the most abundant state of
matter in the universe!!!
Changes of State
HYDROCARBONS
Distillation (Fractionation) Column
Gasoline, kerosene, diesel
fuel, asphalt & tar are
distilled from crude oil.
Chemical Reactions:
Oxidation & Reduction
Chemical Reactions:
Oxidation & Reduction
Rusting = Oxidation
Smelting = Reduction
Chemical Reactions:
Acid & Base Reactions
Chemical Reactions:
Polymerizaton & Depolymerization
Addition Polymerization
Chemical Reactions:
Polymerizaton & Depolymerization
Condensation Polymerization
Materials and the Modern World

Materials define a society’s technical
sophistication

Chemists’ contributions

Properties of Materials
1) The kind of atoms of which it is made
2) Arrangement of atoms
3) Type of bonding of atoms
Different Kinds of Strength
 Strength
 Compressive
 Tensile
 Shear
 Elastic Limit
 Strength depends on the types
and arrangements of bonds
Compressive Strength:
(Strength against squeezing)
 Stack of paper
 Masonry
 Wood
Tensile Strength:
(Strength against pulling)
 Wire
 Rope
 Chains
Shear Strength:
(Strength against twisting)
 Girder network
 Diamond
Composite Materials
 Combination of materials
increases strength
 Reinforced concrete
 Plywood
 Fiberglass
Magnetic Properties of Materials
 Magnetic field
 Due to electrical current
 Electrons spinning
 Arrangement of atomic
magnets
 Degree of alignment
determines the strength
of magnetism
Key Idea
Modern electronics control the flow of electrons
Metals are conductors of electricity, while ionic and
covalently-bonded materials are electrical insulators
2. Semiconductors conduct electricity under carefully
controlled conditions
1.
Key Words
p-type and n-type
diode
integrated circuit
microchip
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.
Semiconductors
 Semiconductors: neither good
conductors nor insulators
 Example: Silicon
Semiconductors: Phosphorus doped
n-type Semiconductors
Dope with phosphorus
One extra electron for each P
Semiconductors: Aluminum doped
p-type Semiconductors
Dope with aluminum
A missing electron = hole
p-type Semiconductors
Dope with aluminum
A missing electron = hole
Diodes
A junction of p- and n-type semiconductors
creates a one-way valve
The Transistor
 Transistor
 Control flow of electrons



Emitter
Base
Collector
 Uses
 Cell phone
 Computer
The Transistor as an Amplifier
Microchips (Integrated Circuits)
 Complex array of p- and n-
type semiconductors
 Designed with layers
interconnected
New materials often lead to new
technologies that change society
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
Two Developing Technologies
 Computers store and manipulate information
 Nanotechnology – the future of materials science