Sodium chloride NaCl has a face-centered cubic FCC crystal structure, also known as the rock salt structure. In this structure, each sodium Na+ ion is surrounded by six chloride Cl- ions, and each chloride ion is surrounded by six sodium ions. The arrangement forms a three-dimensional lattice where the ions are held together by strong ionic bonds.The factors that determine the crystal structure of NaCl are:1. Ionic size: The relative sizes of the sodium and chloride ions play a crucial role in determining the crystal structure. In NaCl, the ratio of the ionic radii r+/r- is approximately 0.55, which is suitable for the formation of a face-centered cubic structure.2. Electrostatic forces: The strong electrostatic attraction between the positively charged sodium ions and the negatively charged chloride ions contributes to the stability of the crystal structure. This ionic bonding leads to the formation of a lattice with alternating positive and negative ions.3. Close packing: The face-centered cubic structure allows for efficient close packing of the ions, which minimizes the energy of the system. In this arrangement, the ions are packed as closely as possible, leading to a high packing efficiency and a stable crystal structure.4. Coordination number: In the NaCl crystal structure, each ion has a coordination number of 6, meaning that it is surrounded by six ions of the opposite charge. This coordination number is a result of the ionic size ratio and the electrostatic forces, and it contributes to the stability of the crystal structure.5. Lattice energy: The lattice energy, which is the energy required to separate the ions in the crystal structure, is another factor that determines the stability of the NaCl crystal structure. The face-centered cubic structure of NaCl has a high lattice energy, indicating strong ionic bonds and a stable crystal structure.