**The most fundamental property of a crystal lattice is its symmetry.
If we initially limit ourselves to 2 dimensions for simplicity, three types
are:**

**Squares**

**Rectangles**

**Hexagons**

**Squares**

**A square lattice may be visualized like this. **

**Each "stuff" represents a unit cell - the unit of repetition in the
crystal.**

**If you were in one of the unit cells and looked out, you would see
the same "stuff" at 0, 90, 180, and 270 degrees because a square
repeats itself at 90 degree intervals - each 1/4 rotation.**

**A rectangular lattice repeats at 0 and 180 degrees. We find "stuff"
farther away at 90 and 270 degrees.**

**A
square "eye" lattice.**

**
A square "foot" lattice.**

**Look again at the "stuffed" hexagons. Notice that the unit
cells completely fill the surface.**

**If the unit cells were seen in 3 dimensions, they would completely
fill the space.**

**This is an important restriction as it prevents certain arrangements
such as pentagonal unit cells, as shown below.**

**Do you see that this type of arrangement is not possible?**

**The unit cells must completely fill the surface and have no
overlap.**

**In 3 dimensions, the ideas are similar; unit cells stack like
boxes, filling the space, making the crystal.**

**The different colors are just to show the separate boxes - each unit
cell is identical.**

**Cubic
Hexagonal**

*Click
here to go to the next page.*

**Structure of Crystals**
**Crystal
Lattices**
**Unit Cells**
**From Unit Cell to Lattice**
**From Lattice to Unit Cell**
**Stoichiometry**
**Packing & Geometry**
**Simple Cubic Metals**
**Close Packed Structures**
**Body Centered Cubic**
**Cesium Chloride**
**Sodium Chloride**
**Rhenium Oxide**
**Niobium Oxide**

*Except as otherwise noted, all images, movies and
VRMLs are owned and copyright
by**Barbara L. Sauls and Frederick C. Sauls 2000.**Contact the owners for individual permission to
use. blsauls@kings.edu*