Crystals and Their Structure

Unit Cells in the Cubic Crystal System

Simple Cubic

Body - Centered Cubic

Face - Centered Cubic

Cubic Closest Packing of Frozen Argon

Cubic Closest Packing of Frozen Methane

Coordination Number

Counting Cell Occupancy

Volume of the Unit Cell r is the radius of an atom in the unit cell r The volume of the unit cell is L 3 L But how do you get L? The Pythagorean Theorem, of course!

Volume of the Unit Cell L L r r r r

Calculating Packing Efficiency L L Packing efficiency is the ratio of the space occupied in the unit cell to the volume of the unit cell Cell occupancy = 4 r r r r

Sodium Chloride

Crystalline and Amorphous Silicon Dioxide Cristobalite, one of the crystalline forms of silicon dioxide, shows cubic closest packing. A glass made from silicon dioxide shows the amorphous disoriented structure.

STM of Silicon

STM of Gold mikro/images/stm.gif 3/27/02

STM Images 3/27/02 Xe atoms on Ni substrate

STM Images 3/27/02 Carbon monoxide on Pt

STM Images 3/27/02 Fe corral on Cu substrate