The cations and anions are arranged in alternate form in :

In an ionic crystal (e.g. NaCl), positive ions (cations) and negative ions (anions) are arranged alternately in a three-dimensional lattice, so that each ion is surrounded by ions of opposite charge.
This arrangement maximises attraction between opposite charges and minimises repulsion between like charges.
Metallic crystals have positive ions in a sea of electrons, and covalent crystals have atoms joined by covalent bonds.
So cations and anions are arranged alternately in an ionic crystal.