Hello students welcome to module number 1 let us discuss something about solid state in this module we will discuss some introduction and classification of solids. My dear students we know that anything which occupied space and has definite mass as known as matter. A matter exist in a 3 physical state the first one is a solid second one is liquid and third one is gas and these three physical state are inter convertible by changing the condition of temperature and pressure the solid on heating it is changes to a liquid. On heating the liquid changes into the gas by cooling the gas is converting to the liquid . and again cooling the liquid changes into the solid . There for the 3 states of matter are interconvertible by change in the temperature or pressure now let us scientist has discovered the two states of matter and these are plasma and Bose–Einstein condensate. The discovery of fifth state of matter was done by a great Indian scientist sattindranath Bose and well known scientist Albert Einstein. These 3 physical state of substance are mainly depends on two factor the first one is inter particles attractive forces and second one is thermal energy. The inter particles attractive forces constant particle tends to keep closer but thermal energy tends to keep them apart. Now students what are the solids the solids are the substance which have definite shape and definite volume. For example the TV, door , laptop these have definite shape and definite volume . These are the examples of the solids. Now what are the general characteristics properties of solids are the first one the solids have fixed mass, shape, volume and density for example this box this box has definite mass definite volume definite mass definite shape also. In solids the intermolecular distance is very small take a look here the particles are closely packed there for intermolecular distance are very small. And if intermolecular distance are very small means what is the force of attraction .the force of attraction that is intermolecular force of attraction is very strong and coming to the last point the solids are hard, rigid and incompressible. These are properties of solid. Now the classification of solids based on the nature of orderly arrangement of constitute particles in 3 dimensions. The solids are classified into two types first one is crystalline solid and second one is amorphous solid now the students what are these crystalline solid and amorphous solid .their a long range orderly arrangement of constituent particles in known as crystalline solid . and there is not long range orderly arrangement of constituent particles are known as amorphous solid .for crystalline solid examples are quartz , sodium chloride etc. for amorphous solid examples are polyvinyl chloride, glass fiber etc. now the properties of crystalline solid the first property is crystalline solids have Sharp melting point and definite heat of fusion why crystalline solids have sharp melting point because the strength of all the bonds between the particles are equal there for crystalline solids have sharp melting point. Ice is an example of crystalline solid the melting point is zero degree Celsius coming to the second property of crystalline solid that is anisotropy. There is many properties which have different values in different directions for example the thermal conductivity , electrical conductivity , reflective index , mechanical strength are different along different directions in one directions the compositions of solid is green purple , green purple and other it is purple, purple, purple, purple since the composition of solid changes with direction has the values of physical properties also changes therefor it exhibit work and isotropy nature or an isotropy now for this plain solid start and is appropriate in nature now what are the differences between crystalline and amorphous solid coming to the first parameter that is arrangement there is a long range orderly arrangement of particles in crystalline solid in case amorphous solid that is short range of orderly arrangement i.e. there is no long range orderly arrangement of particles in case of amorphous solid the second property is melting point crystalline solids are have sharp melting point amorphous solid do not have sharp melting point because the strength of all the bonds between the particles are not equal there for amorphous solid don’t have Sharpe melting point and third property heat of fusion crystalline solids have definite heat of fusion and amorphous solid no definite heat of fusion. And coming to the fourth anisotropy and isotropic nature .the crystalline solids are anisotropic in nature and amorphous solids are isotropic in nature and coming to the fifth point nature. Crystalline solids are also known as true solid and amorphous solids are also known as a pseudo solid and coming to the last point shape crystalline solids have definite geometrical shape but amorphous solid has irregular shape. Thank you students.