In ionic compounds, there are no bonds, but there are a number of interactions. The size of the ions shows the number of possible interactions, and therefore the bigger the cation the higher the number of anions that it can support.
For NaCl, each Sodium ion is surrounded by 6 Chlorine ions while each chlorine ion is surrounded by 6 Sodium ions.
For a bigger cation such as Caesium 8 chlorine atoms surround the cation while 8 Caesium ions surround the anion.
