How would you describe the arrangement of sodium ions and chloride ions in a crystal of sodium chloride?
The sodium and chloride ions in a crystal of sodium chloride form a crystal lattice.
Inside the crystal lattice, each sodium ion,
NaCl has a cubic unit cell. It is best thought of as a face-centered cubic (ffc) array of anions with an interpenetrating fcc cation lattice (or vice-versa).