crystal structure


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What is a Crystal :

What is a Crystal IT is a solid particle which is formed solidification process in which structural units are arranged in particular geometric pattern or lattice this complete process can be stated has crystallization. Formation of crystals involves 3 steps


MECHANISM OF CRYSTALLIZATION SUPERSATURATION : When a solubility of a compound or solute in a solvent exceeds saturation solubility the solution become super saturation and the compound or solute may ppt or crystalize Super saturation can be achieved by: Evaporation of solvent from solution Cooling of solution Addition of substance which is more soluble in solvent than the solid to be crystallized


NUCLEATION Initially formed crystals contain molecular size which are termed as nuclei Nucleation refers to birth of very small bodies within in a homogenous supersaturated liquid phase Crystal growth: It is a diffusion process and surface phenomenon from solution solute molecules reach the phase of crystal by diffusion. On reaching the surface the molecules must be accepted by the crystal organized into space lattice

Mier’s supersaturation theory:

Mier’s supersaturation theory

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This theory postulates a definite relationship between concentration & temperature at which crystals will spontaneously in unseeded solution according to it super solubility curve represents the limit at which nucleus formation begins spontaneously & consequently the point where crystallization begins in the absence of any solid particle

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Crystal lattice : It is defined as an orderly internal arrangement of particles in 3d space

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Crystal habit : the size and shape of crystals in a crystalline solid is know as crystal habit the size and shape of crystals formed depends upon conditions under which crystallization is carried out Ex: grisefulvin from acetone has different form from the same drug crystallized from benzene or chloroform Depending upon arrangement of faces, crystal habits are described in different ways

Crystalline Solid:

Crystalline Solid

Unit Cell:

Unit Cell The smallest component of the crystal (group of atoms, ions or molecules), which when stacked together with pure translational repetition reproduces the whole crystal.

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Reference c v s subrahmanyam lachman

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