# Edge length unit cells ionic crystals

In ionic crystals there are mainly 3 types of structures: Face-centered cubic and octahedral interstices; face-centered cubic with tetrahedral interstices; and body-centered cubic.

My question is how can I know the edge of the unit cell of this crystals for calculating the theoretical density of a crystal?

• Well, you need to know what type of unit cell the lattice is and the ionic radius of the atom. – Nanoputian May 14 '16 at 12:17
• As you see in my question they are all cubic. I know I need to know the ionic radius I'm looking for a formula. For example I know that for Central Cubic Faces $a= 2 (r_{cat} + r_{an})$ – Granger Obliviate May 14 '16 at 12:30
• What is the Spanish word you are thinking of? 'corpse' is not the right translation I think. – bon May 14 '16 at 14:44
• @bon - "cubic with central corpse" = "body-centered cubic (bcc)" – Todd Minehardt May 14 '16 at 15:18
• en.wikipedia.org/wiki/X-ray_crystallography – orthocresol May 14 '16 at 16:36