ENGR 220 Lecture 4 Chapter 2
Week 2 Homework Problems Due Wednesday Chapter 3 3.3, 3.6, 3.7, 3.14
Mixed Primary Bonding A. Very few materials are purely ionic or covalent B. Mixed ionic-covalent bonding is possible 1. Depends on their differences in electronegativity C. Formula 1. lonic Character Formula Primary Bonds A. Ceramics 1. Large bond energy (high bond energy) 2. lonic and Covalent 3. Coalent are directional a) Force can only act between directionally B. Metals 1. Variable bond energy 2. Metallics Secondary Bonding A. Induced-Induced Dipoles 1. Van de Waals Bond B. Weakest of bonds C. Charge displacement 1. Movement of the charges D. Opposite charges attract 1. Still a coulombic attraction formula still works Dipole-Dipole Interaction A. Occurs 1. Between induced dipoles 2. Temporary and fluctuating attractive forces B. Exploited 1. In liquefaction of inert gases C. Asymmetric arrangement of + and - charged regions D. Also Occur 1. Between adjacent polar molecules 2. Stronger than bonds involving induced dipoles E. Hydrogen bond (most important bond) 1. Special type of polar molecule secondary bond a) Strongest secondary bond
11.
1I1.
IV.
b) Explains abnormally high melting temp. V. Properties of Bonding A. Bond Length 1.ro B. Bond Energy 1. E. C. Relative Melting Temp 1. TM D. Coefficient of Thermal Expansion 1. 2. Change in length/original length= (T2-T1) 3. Want alpha to be as small as possible a) More stable if smaller 4. Larger if E. is smaller (shallower) 5. High asymmetry = high alpha E. Stiffness 1. If the bond is strong it will be more stiff 2. Steaper slope stiffer bonds
ENGR 220 Lecture 4 Chapter 3
All sections but 3.11
Quiz next week on chapter 2 and chapter 3 No equation provided
HW Week 3 4.1,4.5,4.6,4.26
The Structure of Crystalline Solids A. How do atoms assemble into solid structures 1. Metals B. How does the density of a material depends on its structure 11. Crystal Structures A. Atomic Arrangements 1. Crystalline Solids a) Long and Short range order b) Metalics and ceramics (1) Single crystals (2) Poly crystals 2. Amorphous Solids a) Short range order only (1) Not organized in a nice "pattern" b) Most Polymers and Inorganic Glasses (1) Window Glass 3. Mixed Crystalline and Amorphous a) Some polymers, glasses, and ceramics II. Crystalline vs Amorphous A. Ceramic Compounds (aka Silica) 1. Can be crystalline or amorphous a) Depends on cooling rate and time (1) More time is more ordered crystalline=quartz (2) Less time random amorphous=fused silica IV. Energy and Packing A. Dense, ordered packing B. Closer Order 1. Denser packing 2. Stronger bonds 3. More stable V. Materials and Packing A. Crystalline Materials 1. Atoms packed in periodic a) Metals b) many ceramics c) Some pol