Solids and classification of Solids
Solids and classification of Solids is a important topic in chemistry. The solids are the substances which have definite volume and definite shape. In terms of kinetic molecular model, solids have regular order of their constituent particles (atoms, molecules or ions). These particles are held together by fairly strong forces, therefore, they are present at fixed positions. The properties of the solids not only depend upon the nature of the constituents but also on their arrangements.
· Definite mass
· Definite volume and shape
· Short intermolecular distance
· Strong intermolecular forces
· Rigid and incompressible
Classification of Solids
Crystalline solids or crystals have ordered structures and symmetry. The atoms, molecules, or ions in crystals are arranged in a particular manner; thus, have a long range order.
In crystalline solids, there is a regular, repeating pattern; thus, we can identify a repeating unit.
By definition, a crystal is “a homogenous chemical compound with a regular and periodic arrangement of atoms.Examples halite, salt (NaCl), and quartz (SiO2). But crystals are not restricted to minerals: they comprise most solid matter such as sugar, cellulose, metals, bones and even DNA.”
Crystals can be categorized according to their physical and chemical properties. They are:
- covalent crystals (e.g.: diamond),
- metallic crystals (e.g.: pyrite),
- crystals ionic crystals (e.g.: sodium chloride) and
- molecular crystals (e.g.: sugar).
Crystals can have different shapes and colors. Crystals have an aesthetic value, and it is believed to have healing properties; thus, people use them to make jewelry.
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Amorphous solid is a solid which lacks a crystalline structure. That is, it does not have long range ordered arrangement of atoms, molecules, or ions within the structure.
Glass, gels, thin films, plastics and nano structures materials are some examples for amorphous solids.
Differences between crystalline and amorphous solids:
|They do not have regular arrangement of particles, therefore do not have well defined particles||They have a regular three dimensional arrangement of atoms, ions or molecules due to which they have well defined geometrical shape|
|They have short range order||They have long range order|
|They do not have sharp melting point i.e., they melt over a range of temperature.||They have sharp melting point i.e., they melt at a particular temperature|
|They do not have fixed heat of fusion.||They have high and fixed heat of fusion, i.e., high energy is required to melt 1 mole of crystalline solid|
|They are isotropic, i.e., they have same properties in all directions.||They are anisotropic , i.e., they have different properties such as optical and electrical properties in different directions.|
|Amorphous solids are unsymmetrical||When crystalline solids are rotated about an axis, their appearance does not change. This shows that thay are symmetrical|
|Amorphous solids don’t break at fixed cleavage planes.||Crystalline solids cleavage along particular direction at fixed cleavage planes|
|They are pseudo – solids, i.e., they do not show all the characteristic properties of solids.||They are true solids, i.e., they show all the characteristic properties of solids|
|Glass, gels, thin films, plastics and nano structures materials are some examples for amorphous solids.||Examples of Crystalline solids are halite, salt (NaCl), and quartz (SiO2).|
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