In chemistry, the coordination number (c.n.) is the sum of the total number of neighbors of a central atom in a chemical compound and the number of lone pairs on it. In methane the coordination number for the carbon atom is 4. In inorganic chemistry the number of sigma bonds between ligand and the central atom count but not the number of pi bonds.

In materials science, the bulk coordination number is the number of atoms touching any other atom in a crystal lattice. It differs from the surface coordination number which is always less than the bulk coordination number. The surface coordination number is dependant on which Miller index the surface uses. In a body-centered cubic (BCC) crystal, the bulk coordination number is 8, whereas for the (100) surface, the surface coordination number is 4.

References

• IUPAC Compendium of Chemical Terminology 2nd Edition (1997)

chemical bonding | Materials science

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