1. The problem statement, all variables and given/known data Calculate the Radius of Rubidium ion (which adopts sodium chloride structure.), if the density of Rubidium chloride is 2.76g*cm^(-3) and if we assume that the ions touch each other along the sides of the edge of the unit cell. I'm a bit lost here. I assume the density is the density of the whole unit cell. But how can I find a radius without knowing any length at all?