From this link: http://www.chemguide.co.uk/atoms/str...nicstruct.html
it explains why NaCl has a 6:6 coordinated structure and not an 8:8 coordinated structure. However, i don't really understand their explanation "Now imagine what would happen if you replaced the caesium ion with the smaller sodium ion. Sodium ions are, of course, smaller than caesium ions because they have fewer layers of electrons around them.
You still have to keep the chloride ions in contact with the sodium. The effect of this would be that the whole arrangement would shrink, bringing the chloride ions into contact with each other - and that introduces repulsion.
However, I don't see how the added repulsion would cause it to align in the 6:6 coordination. Won't all the forces be cancelled out even in that structure (http://postimage.org/image/hushz6i5z/
) drawing the forces in the object, i realized that the forces will cancel out so there is not net force on the whole object. So why can't NaCl form an 8:8 coordinated structure?
Thanks for the help :)