The crystal lattice parameter is 0.563 nm. The diagram shows both a unit cell with ion locations indicated (a) and a space filling model (b) of ionic hard spheres. The cohesive energy of NaCl is - ...

ions. The lattice arrangement continues in three dimensions. This is why solid ionic compounds form crystals with regular shapes.

It is not. A 3D construction model shows how the ions are arranged in a lattice structure. These models usually use coloured balls to represent the ions. Some use sticks to show the ionic bonds.