Crystalline Solids

BLB 12th Chapter 12Sections 1-3, 5

Types of Crystalline Solids p. 464

Macroscopic structure depends upon microscopic structure.

Fluorite (CaF2) Amethyst (SiO2) – quartz+ Fe & Mn

Pyrite (FeS2, 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

edgeface

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

p. 468

Types of cubic unit cells

Body-centered cubic unit cell of C60

Types of cubic unit cells

Three items to determine for each type:1. Number of atoms per unit cell2. Number of nearest neighbors for each atom3. Relationship between sphere radius and the cell edge length, do?

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

Close Packing

Hexagonalclose-packed (hcp)ABAB layers

Cubicclose-packed (ccp)ABCABC layers

Close packing unit cell types

What about the space left over?