ENGR 220 Lecture 5 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
Read Chapter 2 and 3 Read Chapter 4 for prep
Metallic Crystal Structures A. Densely Packed 1. Typically only one element present so all atomic radii are the same 2. Metallic bonding is non-directional B. Number of Atoms (N) Per Unit Cell 1. General Rule for Cubic System 2. Number Interior + Number Face / 2 + Number Corner / 8
11.
Simple Cubic A. Rare due to low packing density 1. Only polonium B. Close packed C. Coordination Number (CN) 1. Number of nearest neighbors 2. For simple cubic CN=6 D. Atomic Packing Factor (APF) 1..52 2. How much space in unit cell has material in it 3. APF=volume of atoms in unit cell + volume of unit cell Body Centered Cubic (BCC) A. Something in the center of the body B. Atoms touch each other along the body diagonals 1. Everything touches only through the unit in the center of the body C. Number of Atoms in unit cell 1. 1 in center + 8 x 1/8 at the corners = 2 Atoms D. CN 1. Eight E. APF 1. .68 2.Close packed direction = 4R=v
UI.
3. (atoms/unit cell)(volume/atom)/volume/unit cell IV. Face Centered Cubic (FCC) A. Atoms touch each other along face diagonals B. Forms an x along the faces C. AI, Cu,Au, Pb, Ni, Pt,Ag D. Number of Atoms in unit cell 1. 4 atoms per unit cell 2. 6 faces x 1/2 + 8 x 1/8 (corners) E. CN 1. 12 2. Also touching in the adjacent unit cell F. APF 1. Face diagonal a) Length=4R= V 2..74 G. Stacking Sequence 1. ABC-ABC stacking sequence V. Hexagonal Close Packed (HCP) A. Top and bottom layers are basal planes B. Stacking Sequence 1. AB-AB C. CN 1. 12 D. APF 1. 0.74 VI. NaCl "RockSalt" Crystal Structure A. FCC-like arrangement of Anions and CAtions at center of cube and at the center of each cube edge 1. VII. Diamond Cubic Crystal Structure A. Ceramic B. Zinc-Blende structure C. FCC-like structure with interior tetrahedral atom positions D. CN 1.4 E. Atoms per Cell 1. 8 atoms/unit ce