What is the coordination number for a lattice point in a body-centered cubic structure?

• A. 4
• B. 6
• C. 12
• D. 8

Answer: (D)

Coordination number is the number of nearest neighboring atoms touching a given atom. In a body-centered cubic lattice, there are atoms at the eight corners of the cube and one atom at the center. The center atom sits equidistant from all eight corner atoms, and these eight corner atoms are the closest neighbors. There are no closer or additional neighbors at the same distance, so the number of nearest neighbors is eight. Thus the coordination number is eight. (Each corner atom also has eight nearest neighbors—the central atoms of the surrounding cubes—this eight-neighbor arrangement is characteristic of BCC, unlike the twelve in FCC or six in simple cubic.)