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Question 3: Distinguish between crystalline, amorphous and polymer solids.


Some definitions and explanations:
(1) Crystal: In simple words, a crystal is a solid in which the atoms or molecules are arranged in a particular way and this arrangement of atoms or molecules is repeated throughout the solid.
(2) Amorphous: Amorphous means a structure which is not regular.
(3) Polymer: Means many parts or many segments.
(4) Solid: Firm and stable in shape and volume.

Crystalline Solids

(1) Those solids whose atoms, ions or molecules are arranged in a regular and repeated manner extending in three dimensions are called crystalline solids.

(2) There are cohesive (attractive) forces among the atoms. Due to the presence of these force, crystalline solids maintain long range orders.

(3) Atoms or molecules of the crystalline solids vibrate about their fixed positions but the cohesive forces do not allow them to leave their positions.

(4) Crystalline solids have definite melting point. The crystal order breaks at this temperature.

(5) Metals like zinc, copper and iron have crystalline structure. Other examples of crystalline solids are NaCl, sucrose and diamond.

Amorphous Solids

(1) Atoms, ions or molecules of amorphous solids do not have definite pattern and are randomly oriented.

(2) Atoms, ions or molecules of amorphous solids have regular arrangement in a small region and are called short order.

(3) Amorphous solids do not have definite melting points.

(4) Glass is an example of amorphous solids.

Polymeric Solids

(1) Polymers consists long chains of organic molecules.

(2) The molecular structure of polymeric solids is more orderly than amorphous solids but less orderly than crystalline solids.

(3) Examples of polymeric solids are rubber, proteins, wool etc. However, artificial polymers are polythene, nylon etc.


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