An FCC (face-centered cubic) crystal is a type of crystal structure in which the lattice points are arranged in a cubic pattern with additional points located in the centers of each face of the cube. This results in a dense and symmetrical arrangement of atoms or molecules.
In an FCC crystal, the nearest neighbors are the atoms or molecules that are closest to a specific point in the lattice. For each lattice point, there are 12 nearest neighbors located at the corners of the cube and 6 on the faces of the cube.
The bond angles in an FCC crystal are determined by the arrangement of nearest neighbors. In an FCC lattice, the angles between atoms or molecules are all equal and measure 90 degrees.
Packing fraction is a measure of how efficiently the atoms or molecules are packed in a crystal structure. For an FCC crystal, the packing fraction is 0.74, meaning that 74% of the available space is occupied by the atoms or molecules.
The FCC crystal structure is one of the most common and densely packed crystal structures. It is similar to the HCP (hexagonal close-packed) structure, but differs in the arrangement of the additional points on the faces of the cube. The BCC (body-centered cubic) structure is less dense and has fewer nearest neighbors compared to the FCC structure.