MTL 200 Chapter Notes - Chapter 3: Metal, Coordination Number, Metallic Bonding

• School: Ryerson University
• Department: Mechanical Engineering
• Course: MTL 200
• Professor: Alan Mac Hin

Document Summary

Dense, ordered structures tend to have lower energies. Crystalline materials - atoms packed in periodic, 3d arrays, ex. Noncrystalline structures have no periodic packing, ex. complex structures, rapid cooling. Metallic crystal structures have the simplest crystal structures and tend to be densely packed. Usually only one element present, so all atomic radii are the same. Nearest neighbour distances tend to be small in order to lower bond energy a=edge of cube cube edges- coordiantion number = 6 (number of nearest neighbors) Electron cloud shields cores from each others. Atomic packing factor = (volume of atoms in unit cell) / (volume of unit cell) Simple cubic structure - rare due to low packing density - close packed directions are. Body centred cubic - atoms touch each other along cube diagonals - coordination. Close packed directions: length = 4r= sqrt(a) Closed packed directions: 4r = 2 (a) Hexagonal close packed structure - abab stacking sequence - coordination number =