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Properties of Solid..........
 LATENT HEAT OF FUSION
    Latent heat of fusion is defined as:
    The amount of heat required to melt unit mass of solid substance at its melting point.
    It is denoted by Hf.
    Unit:
    Its unit is
    J/Kg ,
    erg/gm
    Formula:   Q=m x Hf
    Where
     m= mass of solid
    Q= amount of heat
     UNIT CELL Crystals made of very small basic patterns or arrangements of atoms or molecules or
    ions.These basic patterns are joined together to form a crystal.Theses basic patterns are known
     as "UNIT CELL". All the unit cell of a crystal are identical.

    Characteristics of unit cell

A unit cell has a definite shape.

Length of edges of a unit cell are definite.

Angle between the edges are definite.

All unit cells of a substance always contain equal numbers of atoms or molecules or ions.

    Cell parameters

    Length of edges (axes) and the angle between the edges are collectively known as "Cell Parameters".

    CRYSTAL SYSTEM

    There are seven types of crystals

    1) Cubic Crystal System:

· In cubical crystal system, all the edges are equal

    a = b = c
     angle between the edges are equal i.e. 90

    a = b = g = 90

    Examples:

1. Sodium chloride (NaCl)

2. Zinc sulphide (ZnS)

3. Diamond

 

    2) Tetragonal Crystal System:

· In tetragonal crystal system, two sides are equal but third side is different.

a = b ¹c

· Angles between the edges are equal i.e 90

    a = b = g = 90

    Examples:

1. SnO2

2. BaSO4.4H2O

3) Orthorhombic Crystal System:

· In orthorhombic crystal system, all the edges are different.

a ¹ b¹c

· Angle between the edges are equal i.e 90o

          a = b = g = 90

Example:

1. FeSO4.7H2O

2. ZnSO4.7H2O

3. KNO3

    4) Trigonal Or Rhombohedral Crystal System:

· In this system, all the edges are equal

a = b = c

· angles are equal but not equal to 90o. angles are between 90 and 120

          a = b = g ¹ 90

   Examples:

1. KNO3

2. AgNO3

    5) Hexagonal Crystal System:

    In this system, two sides are equal but third side is different.

a = b ¹ c

    Two angles between the edges are equal to 90o but third angle is equal to 120.

         a = b = 90, g = 120

    Examples:

    Graphite

    6) Monoclinic Crystal System:

· In monoclinic crystal system, all the edges are different

a ¹ b ¹ c

· two angles are equal to 90 but third angle is not equal to 90

a = g = 90

            b ¹ 90

    Examples:

1. CuSO4. 5H2O

2. Sugar

7) Triclinic Crystal System:

in this system, all the edges are different

a ¹ b ¹ c

angles between the edges are not equal to 90

a ¹ b ¹ g ¹ 90

Examples:

1. CuSO4. 5H2O

              2. K2Cr2O7

    
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