Lets look at the difference between Cesium Chloride and sodium chloride, both of which are alkaline chlorides.
Relating to unit cells, the ionic structures depend on the cation vs anion size. For example, for CsCl it is primitive cubic, Cs+ in the center was Cl- on the corners. NaCl is FCC with Na+ in the 8 holes, Cl- ions are much bigger than Na+ so sodium fits into the holes left by chlorine. CaF2 is also FCC with tetrahedral holes Ca2+ fits into the gaps left by Flourine.
Each cubic cell has 8 atoms in each corner of the cube, and that atom is shared with 8 neighboring cells. In the Body Centered Cubic Cell (BCC) there is an additional atom in the center of the cube, and in the face centered cubic cell, an atom is shared between two unit cells along the face.
Figure12.1.112.1.1\PageIndex{1}: The 7 types of unit cells. In this class we will only look at cubic systems, and will identify 3 types of cubic unit cells (figure. 12.b)
αα\large\alpha = angle in the yz plane ββ\large\beta = angle in the xz plane γγ\large\gamma = angle in the xy plane