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The accomplishment of any project work depends on the cooperation, coordination and united efforts of several sources of material, knowledge and time. Hence this opportunity is taken to express my appreciation to all the people for completion of this project.
I express my deep gratitude to my project guide Mrs. Y. Dewan, PGT Chemistry, who has been kind enough to render this valuable guidance in spite of her many preoccupations, in the preparation of this project.
I am grateful to this staff of science section of our school for the help. I am also thankful to all the colleagues who helped me in this ...view middle of the document...
They are crystalline and amorphous. They have differences that are very important in the study of Physical Pharmacy. They differ in the way they are arranged, their melting points, and the way they should be treated when used in making drugs.
Crystalline solids are arranged in fixed geometric patterns or lattices. Examples of crystalline solids are ice, methanol, and sodium chloride. They have an orderly arranged units and are practically incompressible. Crystalline solids also show a definite melting point and so they pass rather sharply from solid to liquid state. There are various crystalline forms which are divided into six crystal systems or shapes. They are cubic, tetragonal, hexagonal, rhombic, monoclinic, and triclinic. The units that constitute these systems can be atoms, molecules, or ions. Ionic and atomic crystals are hard and brittle with high melting points. Molecular crystals are soft and have low melting points. Metallic crystals are composed of positively charged ions in a field of electron gas or freely moving electrons. Metals are good conductors of electricity because of the free movement of electrons in the lattice.
Amorphous solids are solids with random unoriented molecules. Examples of amorphous solids are glass and plastic. They are considered super cooled liquids in which the molecules are arranged in a random manner some what as in the liquid state. Amorphous solids also unlike crystalline solids do not have definite melting points.
The difference between an amorphous and crystalline solids is very important in drug making. When making a drug in solution, the drug is added to the other chemicals to prolong the shelf life. When the drug is crystallizing, if it forms a crystalline solid, there is space in the crystal for the ice to come out leaving the drug and the components. This process only takes about two or three days. If the drug forms an amorphous solid during the crystallizing phase then it takes about seven days. This is because amorphous solids do not have space for the ice to come out during the freezing therefore the ice must diffuse out. Therefore it is preferable to have crystalline solids in drug making.
Types of Crystalline Solids:
Crystalline solids may be classified into four types depending upon the nature of bonds present in them.
1) Molecular crystals
In molecular crystals, the constituent particles are molecules. These molecules are held together by weak forces known as Van der Waal’s forces. Common examples are dry ice, wax, iodine, sulphur, etc.
Characteristic features of molecular crystals are:
❖ Molecular crystals are soft, compressible and can be distorted very easily.
❖ They have low melting and boiling points.
❖ These are bad conductors of electricity and are regarded as electrical insulators.
❖ They are volatile and have low heats of vaporization and low enthapy of fusion.