CHM 2045 Lecture Notes - Lecture 32: Covalent Bond, Cubic Crystal System, Atomic Radius
28 Feb 2017
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Document Summary
Crystalline solids possess rigid and long range order. Molecules and ions occupy specific and predictable positions. Amorphous solid does not possess a well-defined arrangement and long range molecular order. Unit cell basic repeating structural unit of a crystalline solid: lattice points corners of unit cells. Lps made up of ion, atoms, or molecules: seven types of unit cells. Simple cubic one particle per unit cell(in the center: packing efficiency of 52, coordination number 6 (number of particles touching center particle, 1 full atom per unit cell. Body-centered cubic 2 particles per unit cell: packing efficiency of 68, coordination number 8, 2 full atoms per unit cell. Face-centered cubic 7 particles per unit cell: packing efficiency of 74, coordination number 12, 4 full atoms per unit cell. Relationship between atomic radius and edge length(a) in three different unit cells. Simple cubic cell: a = 2r, r = a/2.
