Body Centred Cubic
This arrangement of spheres (or atoms) is not exactly close packed. This structure can be obtained if spheres in the first layer (A) of close packing are slightly opened up. As a result none of these spheres are in contact with each other. The second layer of spheres (B) can be placed on top of the first layer so that each sphere of the second layer is in contact with four spheres of the layer below it. Successive building of the third will be exactly like the first layer. If this pattern of building layers is repeated infinitely we get an arrangement as shown in figure. This arrangement is found in Li, Na, K, Rb, Ba, Cs, V, Nb, Cr, Mo, Fe.
Table: Comparison of hcp, ccp and bcc
|Arrangement of packing||Close packed||Close packed||Not close packed|
|Type of packing||AB AB A...||ABC ABC A...||AB AB A...|
|Available space occupied||74%||74%||68%|
|Malleability and ductility||Less malleable, hard, brittle||Malleable and ductile|