solid Solid type explaination

solid  Solid type explainarion

From our earlier studies, we know that  liquids and gases are called fluids because of their ability to flow. 

The fluidity in both of these states is due to the fact that the
molecules are free to move about. On the contrary, the constituent particles in solids have fixed positions and can only oscillate about their mean positions. This
explains the rigidity in solids. These properties depend upon the nature of constituent particles and the binding
forces operating between them. The correlation between structure and properties helps in the discovery of new
solid materials with desired properties. For example,carbon nanotubes are new materials that have potential
to provide material that are tougher than steel, lighter than aluminium and have more conductive property than
copper. Such materials may play an expanding role in future development of science and society. Some other
materials which are expected to play an important role in future are high temperature superconductors,
magnetic materials, biodegradable polymers for packaging, biocompliant solids for surgical implants, etc.
Thus, the study of this state becomes more important in the present scenario.
In this Unit, we shall discuss different possible arrangements of particles resulting in several types of structures and explore why different arrangements of
structural units lend different properties to solids. We will also learn how these properties get modified due to
the structural imperfections or by the presence of impurities in minute amounts.

General General
Characteristics
of Solid State:- 

(i) They have definite mass, volume and shape.

(ii) Intermolecular distances are short.

(iii) Intermolecular forces are strong.

(iv) Their constituent particles (atoms, molecules or ions) have fixed

positions and can only oscillate about their mean positions.

(v) They are incompressible and rigid.

Type of solids:- 

A)Crystalline :- A crystalline solid usually consists of a large number of small crystals,

each of them having a definite characteristic geometrical shape. The

arrangement of constituent particles (atoms, molecules or ions) in a crystal

is ordered and repetitive in three dimensions. 

B) Amorphous:- Amorphous solids are isotropic in nature. Their properties such as

mechanical strength, refractive index and electrical conductivity, etc., are same in all directions. It is because there is no long range order in them and arrangement of particles is not definite along all the directions. 

A)Crystalline solid :-

Crystalline solids can be classified in various ways. The method

depends on the purpose in hand. Here, we will classify crystalline solids

on the basis of nature of intermolecular forces or bonds that hold the

constituent particles together.

 These are — (i) Van der waals forces

(ii) Ionic bonds

(iii) Covalent bonds  

 (iv) Metallic bonds. On this basis,

crystalline solids are classified into four categories 

 molecular,

 ionic,

metallic 

 covalent solids  

Let us now learn about these categories.

Molecular Solids :- 

Molecules are the constituent particles of molecular solids. These are

further sub divided into the following categories:

(i) Non polar Molecular Solids: They comprise either atoms, for example,

argon and helium or the molecules formed by non polar covalent 

bonds, for 

example, H2

, Cl2

 and I2

. In these solids, the atoms or

molecules are held by weak dispersion forces or London forces

about which you have learnt in Class XI. These solids are soft and

non-conductors of electricity. They have low melting points and are

usually in liquid or gaseous state at room temperature and pressure.

(ii) Polar Molecular Solids: The molecules of substances like HCl, SO2,

etc. are formed by polar covalent bonds. The molecules in such

solids are held together by relatively stronger dipole-dipole

interactions. These solids are soft and non-conductors of electricity.

Their melting points are higher than those of non polar molecular

solids yet most of these are gases or liquids under room

temperature and pressure. Solid SO2

 and solid NH3

 are some

examples of such solids.

(iii) Hydrogen Bonded Molecular Solids: The molecules of such solids

contain polar covalent bonds between H and F, O or N atoms.

Strong hydrogen bonding binds molecules of such solids like H2O

(ice). They are non-conductors of electricity. Generally they are

volatile liquids or soft solids under room temperature and pressure.

Ionic Solids :- 

Ions are the constituent particles of ionic solids. Such solids are formed

by the three dimensional arrangements of cations and anions bound

by strong coulombic (electrostatic) forces. These solids are hard and

brittle in nature. They have high melting and boiling points. Since the

ions are not free to move about, they are electrical insulators in the

solid state. However, in the molten state or when dissolved in water,

the ions become free to move about and they conduct electricity.

Metallic Solids :- 

Metals are orderly collection of positive ions surrounded by and held

together by a sea of free electrons. These electrons are mobile and are

evenly spread out throughout the crystal. Each metal atom contributes

one or more electrons towards this sea of mobile electrons. These free

and mobile electrons are responsible for high electrical and thermal

conductivity of metals. When an electric field is applied, these electrons

flow through the network of positive ions. Similarly, when heat is

supplied to one portion of a metal, the thermal energy is uniformly

spread throughout by free electrons. Another important characteristic

of metals is their lustre and colour in certain cases. This is also due

to the presence of free electrons in them. Metals are highly malleable

and ductile.

Covalent or Network Solids:- 

A wide variety of crystalline solids of non-metals result from the

formation of covalent bonds between adjacent atoms throughout the

crystal. They are also called giant molecules. Covalent bonds are

strong and directional in nature, therefore atoms are held very strongly

at their positions. Such solids are very hard and brittle. They have

extremely high melting points and may even decompose before melting.

They are insulators and do not conduct electricity. Diamond (Fig. 1.3)

and silicon carbide are typical examples of such solids. Although

Graphite also belongs to this class of crystals, but it is soft

and is a conductor of electricity. Its exceptional properties are due to its typical structure. Carbon

atoms are arranged in

different layers and each

atom is covalently bonded to

three of its neighbouring

atoms in the same layer. The

fourth valence electron of

each atom is present

between different layers and

is free to move about. These

free electrons make graphite

a good conductor of

electricity. Different layers

can slide one over the other.

This makes graphite a soft

solid and a good solid

lubricant.

KNOW about more :- 

Crystalline solids:-

Solids can be classified as crystalline or amorphous on the basis of the

nature of order present in the arrangement of their constituent particles.

A crystalline solid usually consists of a large number of small crystals,

each of them having a definite characteristic geometrical shape. The

arrangement of constituent particles (atoms, molecules or ions) in a crystal

is ordered and repetitive in three dimensions. If we observe the pattern in

one region of the crystal, we can predict accurately the position of particles

in any other region of the crystal however far they may be from the place

of observation. Thus, crystal has a long range order which means that

there is a regular pattern of arrangement of particles which repeats itself

periodically over the entire crystal. Sodium chloride and quartz are typical

examples of crystalline solids. Glass, rubber and many plastics do not

form crystals when their liquids solidify on cooling. These are called

Amorphous Solids.

 The term amorphous comes from the Greek word

amorphos, meaning no form.The arrangement of constituent particles

(atoms, molecules or ions) in such a solid has only short range order. In

such an arrangement, a regular and

periodically repeating pattern is observed

over short distances only. Regular patterns

are scattered and in between the

arrangement is disordered. The structures

of quartz (crystalline) and quartz glass

(amorphous) are shown in Fig. 1.1 (a) and

(b) respectively. While the two structures

are almost identical, yet in the case of

amorphous quartz glass there is no long

range order. The structure of amorphous

solids is similar to that of liquids. Due to

the differences in the arrangement of the

constituent particles, the two types of solids differ in their properties.

Amorphous solids are isotropic in nature. Their properties such as

mechanical strength, refractive index and electrical conductivity, etc.,

are same in all directions. It is because there is no long range order in

them and arrangement of particles is not definite along all the directions.

Hence, the overall arrangement becomes equivalent in all directions.

Therefore, value of any physical property would be same along

any direction.

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