Close Packing | Chemistry, The Solid State | Note For Science

Close Packing In One Dimension

It is the one way arrangement of particles in which the particle is in constant with its neighbours.

Coordination Number

The total number of atoms directly attached to a single atom called coordination number.

Example:- coordination number of close packing structure in one dimension is 2.

Close Packing Structure In Two Dimension

It can be done in two different ways:- 

a) The second row may be placed in contact with the first row such that the spheres of the second row are exactly above the spheres of the first row. Here we have $AAA$ types arrangement. This packing is called a square close packing in two dimensions here the coordination number is 4.

b) The second row may be placed in contact with the first row such that the spheres of the second row are in the depression of the first row and we have ABAB-type arrangement. This is called hexagonal close packing in two dimension. Here the coordination number is $6$.

Close Packed Structure Coordination Number

Simple Cubic (SC) Lattice: $6$
Body Centred Cubic (BCC) Lattice: $8$
Face Centred Cubic (FCC) Lattice: $12$

Cubic Closed Packing (CCP) or Hexagonal Cubic Packing (HCP): $12$

Voids or Holes or Interstitial Sites

The vacant or empty space in the crystal lattice are called voids.

There are two types of voids:

i) Whenever a sphere of second layer is placed above the triangular voids of first layer. Then a void is formed called Tetrahedral Void.

ii) Whenever a triangular void of second layer is placed above the triangular void of first layer. So that the spheres are do not overlapes, a void is form called octahedral void.

If the number of closed packed sphere is N then the number of octahedral voids is N and the number of tetrahedral voids is 2N.

Question: A compound is formed by two elements X and Y. Atoms of the element Y (as anions) make ccp and those of the element X (as cations) occupy all the octahedral voids. What is the formula of the compound?

Ans will be updated soon kindly keep visiting this blog.

Question: Atoms of element B form hcp lattice and those of the element A occupy 2/3rd of tetrahedral voids. What is the formula of the compound formed by the elements A and B?

Ans will be updated soon kindly keep visiting this blog.