Page 4 - Lesson Note 2

In this arrangement each sphere is in contact with two spheres.

So its co-ordination number is 2.

(b) Close packing in two dimensions: It is of two types.

(i) Two dimensional square close packing:

In this arrangement, each sphere is in contact with four

other spheres. So its co-ordination number is 4.It has

AAAA type of arrangement.

(ii) Two dimensional hexagonal close packing:
In this arrangement, each sphere is in contact with six

other spheres. So its co-ordination number is 6.It has

ABAB type of arrangement.

(C) Close packing in three dimensions: It is of two types.

(i) From two dimensional square close-packed layers:

This lattice has AAAA….. type pattern. The lattice is simple

cubic lattice and its unit cell is primitive cubic unit cell. Its

co-ordination number is 6.