# Coordination number for fcc

1. May 19, 2012

### Woopydalan

When doing these coordination numbers, which atom do I consider? Am I supposed to use only one unit cell to determine the number? When counting the number of nearest neighbors, does it mean literally that only the number of atoms with the shortest distance can be counted, meaning you find the closest neighbor, and only neighbors that are that same distance can be counted?

I can't figure out how sc, bcc, and fcc have numbers of 6, 8, and 12 respectively

2. May 20, 2012

### Infinitum

Hi Woopydalan!

Any atom, the simple structures(similar atom structure) have same co-ordination number for each atom.

No, you have to consider all the nearest atoms to your selected atom, across all unit cells.

Yes.

Try drawing out each structure and find all possible neighbors for each. I'll try explaining SC. For this, consider one atom at the vertex of the unit cell cube. There are three atoms near this atom, on x,y,z axes IN that unit cell. There are also atoms on the -x, -y, -z axes of different unit cells. That makes 6 atoms in total, which is the co-ordination number.

3. May 20, 2012

### Acut

Get a model of those structures. There are some animations online, I'm sure, but physical models work best.