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Sunday, March 18, 2012

Structure of solids

Structure of solids: Matter exists in nature in three states, namely solid, liquid and gas. The atoms, ions or molecules of matter are held together by the force of attraction. These attractive forces which hold constituent particles of a substance together is known as binding forces or bonds. These bonds are quite weak in case of liquids and gases but quite strong in case of solids. If a solid is heated, it doesn’t change its shape easily which simply indicates that particles of solids are bound together by very strong binding forces. The solids are characterized by a definite shape as well as a definite volume. Depending upon the nature and arrangement of atoms or molecules, solids are broadly classified into following two categories:

Geo – thermal (geo-thermal means earth –heat): The earth has three layers i.e. the core, the mental and the crust. The core is the central part of the earth which is surrounded by the mantle. The mantle is surrounded by the uppermost layer of the earth called the crust. The mantle of the earth has molten mass called magma. This magma consists of molten rocks, gases and steam at very high temperature. Due to some geological changes, the hot magma rises up and is collected in the crust of the earth. The region in the crust where the hot magma is collected are called hot spots. The heat energy stored in the hot sports of the earth’s crust is called geo-thermal energy. This energy heats the underground water. The hot underground water comes automatically out of the earth’s surface in certain region where crust is weak in the form of fountains known as water hot water springs or geysers. Geo thermal energy can be converted continuously into electricity for 24 hours throughout the year. Geo thermal energy causes no pollution, so it is environment friendly. The cost of converting geo thermal energy into electricity is very less. 1.       Crystalline solids: crystalline solids are those solids in which the atoms, molecules or ions which constitute the solids, are arranged in a definite pattern in three dimensions throughout the solids. Crystalline solids posses the following characteristics:
                                 i.            The atoms and molecules are arranged in a definite order, giving them a definite order, giving them a definite geometrical form.
                               ii.            They exhibit long range order.
                              iii.            They are bound by flat surface.
                             iv.            They have homogeneous composition.
                               v.            They have sharp melting point and boiling point.
                             vi.            They are anisotropic.
                            vii.            All the bonds in the crystalline solids are equally strong.
2.       Amorphous solids: amorphous solids are those solids in which the atoms are not arranged in regular geometrical pattern. Ordinary glass, sulphur, plastics etc are examples of amorphous solids. Amorphous solids posses the following characteristics:
                                  I.            They do not posses characteristic geometrical shapes.
                                II.            Atoms or molecules of amorphous solids are arranged in irregular ways.
                              III.            They exhibit short range order.
                              IV.            Their composition may not be homogeneous.
                                V.            They are isotropic, so they have same physical properties in all direction.
                              VI.            They do not have sharp melting point.
                            VII.            Bonds between different atoms are not identical.

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