Solid State[part=2]CLASS==12

TYPES OF SOLID

Solid are of two types................


[1]=Crystaline solid




[2]=Amorphous solid




A crystalline solid is a substance whose constituent particles possess regular orderly arrangement 

e.g.= Sodium chloride, sucrose, diamond etc.



An amorphous solid is a substance whose constituent particles do not possess a regular orderly arrangement.


e.g.= glass, plastics, rubber, starch, and proteins.



Amorphous substances are also, sometimes, referred to as super cooled liquids because they posses disorderly arrangement like liquids.



 In fact many amorphous solids such as glass are capable flowing.


  




Uses of Amorphous Solids


Amorphous solids such as glass and plastics are very important materials and are widely used in construction, house ware, laboratory ware etc.




Amorphous silica is likely to be the best material for converting sunlight into electricity (photovoltaic).




Another well known amorphous solid is rubber which is used in making tyres shoes soles etc.



Classification of Crystalline Solids based on Different Binding Forces  




Crystalline solids can be classified into different categories depending upon the type of constituent particles and the nature of attractive forces operating between them.
 



Atomic Solids




In these solids the constituent particles are atoms. These closely packed atoms are held up by London dispersion forces.



Some examples are crystals of noble gases. Such solids are very soft, possess very low melting points and poor conductors of heat and electricity.

  

Molecular Solids




In these solids, the constituent particles which pack up together are molecules of the substance.



These molecules may be non – polar (dipole moment = 0) such as etc. or they may be polar (dipole moment > 0) like etc.

  

In case of non – polar molecules, the attractive forces operating between the molecules are Vander Waal forces (also called dispersion forces).



The example of such solids are : dry ice (Solid, iodine (crystals).

  

In case of polar molecules, the attractive forces operating between the molecules in solid state are dipole – dipole forces.



The examples of such solids are : solid, solid HCl. However, in some solids with polar molecules, the interparticle forces are hydrogen bonds.



The examples of such solids are ice; solid hydrogen fluoride (HF); solid ammonia, etc.  



Characteristics of Molecular Solids





Some of the general characteristics of molecular solids are :

  

They are generally soft.

  

Their melting points are low to moderately high.

The melting points of solids with non – polar molecules are relatively low whereas solids with polar molecules have moderately high melting points.


They are generally bad conductors of heat and electricity.




They have generally low density.





Ionic Solids




In ionic solids, the constituent particles are ions of opposite charges. Each ion is surrounded by a definite number of ions of opposite charge.





The number of ions that surround a particular ion of opposite charge its called coordination number of the ion.



For example, in sodium chloride crystal each sodium ion is surrounded by six chloride ions.



 Hence coordination number of  is 6. At the same time each chloride ion is surrounded by six  ions.



Therefore the co ordination number of ion is also 6.



The interparticle forces in ionic solids are ionic bonds operating between the ions of opposite charges.



some examples of ionic solids are : sodium chloride (NaCl) ; ceasium chloride (CsCl), zinc sulphide (ZnS), calcium fluoride, etc.




Characteristics of Ionic Solids





Some common characteristics of ionic solids are as follows:




They are hard, brittle and have low volatility




They have high melting points.




They are poor conductors of electricity in solid state, however they become good conductors of electricity in molten state or in dissolved state.




They are generally soluble in polar solvents like water.





Covalent Solids




In these types of solids the constituent particles are atoms of same or different elements connected to each other by covalent bond network.




For example, in diamond only carbon atoms constitute the covalent network .




These solids are also called network solids because the covalent bonds extend in three dimensions forming a giant interlocking structure.



Some examples of covalent solids are :

Diamond, silicon carbide, aluminium nitrite etc.




Characteristics of Covalent Solids




Some common characteristics of covalent solids are :





They are very hard. Diamond is the hardest naturally occurring substance.




They have very high melting points.




They are poor conductors of heat and electricity.




They have high heats of fusion.





Metallic Solids




In these type of solids, the constituent particles are metal atoms.



 The interparticle forces in these solids are metallic bonds.



 In the metallic crystals the metal atoms occupy the fixed positions but their valence electrons are mobile.



The attractive force between the kernels and mobile valence electrons is termed as metallic bond.




Characteristics of Metallic Solids





The common characteristics of metallic solids are as follows:




They generally range from soft to very hard.




They are malleable and ductile.




They are good conductors of heat and electricity.




They possess bright lustre.




They have high melting and boiling points.


They have moderate heats of fusion.




The summary of classification of solids on the basis of interparticle forces is given in