Body Centred Cubic

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

Property

 hcp

 ccp

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%

Coordination number

12

12

8  

Malleability and ductility

Less malleable, hard, brittle

Malleable  and ductile

 

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