Which of the following is not a standard coordination number for common crystal lattices?

• A. 6
• B. 8
• C. 12
• D. 14

Answer: (D)

Coordination number is the number of nearest neighbors surrounding a given atom in a crystal. In the common crystal lattices, the typical values are 6 for simple cubic, 8 for body-centered cubic, and 12 for the close-packed arrangements (face-centered cubic and hexagonal close-packed). These numbers arise from how the spheres pack together in those structures: simple cubic has each atom touching six along the axes, body-centered adds the center atom for eight, and close-packed structures allow twelve close contacts. A coordination number of 14 isn’t produced by these standard lattices, so it isn’t a typical or standard value for common crystal structures.