Question

1. What is meant by the term coordination number?

2. What is the coordination number of atoms :

• In a cubic close-packed lattice? 
• In a body-centred cubic structure?  

Answer 1

1. The number of nearest neighbours in a packing is called coordination number.

2. The coordination number of atoms

• In cubic-close packed structure each atom is in direct contact with12 other atoms. Hence, its coordination number is 12.
• In a body centred cubic structure coordination number is 8