Difference between bond length and lattice constant

[sir_manning]

Can anyone explain to me the difference between the bond length and the lattice constant? I'm thinking specifically about cubic crystal systems. Thanks.

-Alan

 

[Mapes]

The lattice constant is the side length of the cube. But the bond length corresponds to the distance between neighbor atoms along the axis of closest packing, which isn't always the side length. In fcc crystals, the closest packing is in the [110] direction; in bcc, the [111] direction.