CsCl is NOT BCC — this is a common trap! BCC means all lattice points are identical. In CsCl, Cs+ and Cl- are different ions. The lattice is simple cubic (Cl- at corners), with Cs+ at the body centre (or vice versa). Z = 1 (1 Cl- from 8 x 1/8, 1 Cs+ from body centre). CN = 8:8 (cubic). Body diagonal = a*sqrt(3) = 2(r+ + r-). Examples: CsCl, CsBr, CsI. At high temperature, CsCl can transform to NaCl structure.