Which lattice type has a coordination number of 8?

• A. FCC
• B. BCC
• C. HCP
• D. Diamond cubic

Answer: (B)

Coordination number is the number of nearest neighbor atoms surrounding a given atom in the crystal. In a body-centered cubic lattice, there are atoms at the eight corners of a cube and one at the center. The central atom lies touching each of the eight corner atoms, giving it eight nearest neighbors. Hence the coordination number is eight for this structure. By contrast, face-centered cubic and hexagonal close-packed lattices have more neighbors (twelve) because atoms touch along face diagonals in a close-packed arrangement, while diamond cubic has only four due to tetrahedral bonding. So eight neighbors point to the body-centered cubic structure.