Crystalline Solids BLB 12 th Chapter 12 Sections 1-3, 5

Types of Crystalline Solidsp. 464

Macroscopic structure depends upon microscopic structure.

Fluorite (CaF 2 )Amethyst (SiO 2 ) – quartz + Fe & Mn Pyrite (FeS 2, fool’s gold)

Crystalline – atoms, ions, or molecules arranged orderly –Ionic compounds, diamond, sugar, ice Amorphous – “without form”; lack the order of solids –Glass, plastic, wax, ceramics

Crystal Terms Crystal – Crytal Lattice – Unit cell – Cell dimensions – a, b, c, α, β, γ corner edge face

Crystalline lattice in two dimensions

Crystalline lattice in three dimensions

Filling the unit cell

Types of Unit Cells

Atoms and ions are represented by spheres. The spheres stack in different patterns three- dimensionally. The close packing of spheres maximizes intermolecular force. The patterns of stacking result in different types of unit cells and lattices. Packing in Crystals

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Types of cubic unit cells

Body-centered cubic unit cell of C 60

Types of cubic unit cells Three items to determine for each type: 1.Number of atoms per unit cell 2.Number of nearest neighbors for each atom 3.Relationship between sphere radius and the cell edge length, d o ?

Primitive (simple) Cubic _______ atoms per unit cell _______ nearest neighbors

Body-centered Cubic _______ atoms per unit cell _______ nearest neighbors

Face-centered Cubic (result of close packing) _______ atoms per unit cell _______ nearest neighbors

Close packing

Close Packing Hexagonal close-packed (hcp) ABAB layers Cubic close-packed (ccp) ABCABC layers

Close packing unit cell types

What about the space left over?