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

Tonight’s Outline Review Chemical Bonding Chemical Reactions Properties of Materials States of matter Changes of state Strength of materials 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 bonds. 3. Ionic, metallic, and covalent bonds

Ionic Bonding

Ionic Bonding Ionic Bonding Na Cl

Ionic Bonding

Ionic Bonding

Ionic Bonding Mg + 2Cl MgCl2 Mg + 2Cl

Ionic Bonding Fluorite CaF2

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

Metallic Bonding

Metallic Bonding

Metallic Bonding

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

Covalent Bonding

Covalent Bonding Hydrogen

Covalent Bonding

Covalent Bonding WATER

Covalent Bonding

Covalent Bonding: Carbon 4 2 C 3 1 (R)-enantiomer CARBON BONDING Organic Chemistry

Covalent Bonding: Carbon 4 2 C 3 1 (R)-enantiomer CARBON BONDING Organic Chemistry

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

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

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: 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 result from: The kind of atoms of which it is made The arrangement of those atoms Type of bonding between those atoms

Different Kinds of Strength Compressive Tensile Shear Elastic Limit = the breaking point 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 Fiberglass Plywood

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

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: 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

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

The Transistor Transistor Uses Control flow of electrons Cell phone 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 many interconnected domains

Microchips and the Information Revolution 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