Packing in the Crystalline Solids: The arrangement of the constituent particles like atoms, ions or molecules at various positions of lattice points within the unit cell of the crystal lattice is called packing in the crystalline. During the formation of crystals, the constituent particles get closely packed together. The particles in any crystal tend to get closely packed together as closely as possible. The closer the packing, the greater is the stability of the closely packed structure. The mod of the packing depends upon the nature, shape, size and polarity of the particles. To start with we describe the packing of equal sized spherical particles.
The Principles of Packing in Solids are as follows:
- 1} In the crystal, particles occupy the lattice points in the crystal lattice.
- 2} In the formation of crystals, the constituent particles like atoms, ions or molecules try to get closely packed together giving, maximum possible closet packing structures.
- 3} The closely packed arrangements are such that maximum available space in the crystal lattice is occupied by constituent particles, so that minimum vacant space is left.
- 4} This arrangement of packing results in maximum possible density of the crystal.
- 5} Closer the packing, more is stability of the crystalline structure.
Packing Fraction: The fraction of the total space in unit cell occupied by the constituent particles is called packing fraction. The extent of packing of constituent particles like atoms, ions or molecules in the unit cell is expressed in terms of packing fraction.
It is the volume occupied by constituent particles per unit cell.
Packing Fraction = Volume occupied by all constituent particles / Volume of the unit cell.
Packing Efficiency: It is the percentage of total space in the unit cell occupied by the constituent particles like atoms, ions or molecules of the crystal.Packing efficiency describes the extent of packing of constituent particles in the unit cell.
Packing Efficiency = (Volume occupied by all constituent particles / Volume of the unit cell) × 100
= Packing Fraction × 100.