Q.3 What is the coordination number? Explain your answer with the help of a sketch, taking the example of a simple cubic lattice. (AKTU. 2010 - 11)
Ans. Coordination Number: -
Each atom in a crystal is surrounded by a number of atoms. The surrounding atoms are located at different distances. The coordination number is defined as the numbr of nearest and equidistant atoms with respect to any other atom in a unit cell. Take for example atom A as reference atom in the unit cell of figure which is simple cube (SC). The atoms marked 1, 2 and 3 belonging to the same unit cell are nearest and equidistant to atom A. The atoms 4, 5 and 6 in the neighbouring unit cells are also exactly nearest and equidistant as atoms 1, 2 and 3. The atoms marked 7, 8, 9 and 10 are not the nearest with respect to atom A. In this way, there are 6 atoms nearest and equidistant with respect to any other atom. Hence coordination number is 6 in case of simple cube (SC).
Q.4 Find the Relation Between Atomic Radius and Lattice Content.
Ans. Relation Between Atomic Radius And Lattice Constant of SC, FCC And BCC: -
Atoms in the unit cells are assumed to be rigid spheres in contact.
Simple Cube (SC): -
