Solid State

solid state

Behaviors of Solid:

           

            The solids have the following properties and characteristics due to which they are easily distinguished from liquid and gases.

i. Compressibility:

            The compressibility of solids is nearly zero, because the particles in solid are closely packed and so tightly bound together that no                inter-spaces are left. Hence the density of solids is much higher than gases and liquids.

ii. Deformity:

            Solids are deformed or shattered by higher pressure. This is because, when some particles are dislocated the forces of attraction is so strong that the rearranged atoms are held equally well to their new neighbours.

iii. Diffusibility:

            Diffusion is very slow in solids when compared with liquids and gases. There is no free movement of the particles but there is only vibration about the mean position e.g. Zn & Cu sheets when placed in close contact for a long time, they diffuse into each other in very slight ratio.

iv. Melting:

            On heating the solids change to liquid state and they melts.

In terms of Kinetic Theory when solids are heated, vibrational energy of their particles increases; until at melting point, some particles are vibrating with sufficient energy to overcome the forces holding them, hence they become mobile i.e. Solid fuse.

v. Sublimation:

            There are some solids substances as camphor iodine, naphthalene etc, which change directly to vapour on heating without passing through liquid phase. This phenomenon is called Sublimation.

In terms of Kinetic Theory, the inter-molecular force in which solids is less ordinary solids, hence high energy molecules at solid surface overcome the attractive forces and directly pass into vapours.

vi. Latent Heat of Fusion:

            Latent Heat of fusion is the heat energy which is required to change  1 gram of a solid into liquid at its melting point e.g. 1 gm of ice at 0 ^oC requires 334 J of heat energy to convert ice completely into water. Hence 334 J is called Latent Heat of fusion of ice.

Classification of Solids:

            There are two main types of solids which are as follows:

§     Crystalline Solid

§     Amorphous Solid

1. Crystalline Solid:

            The solids which have very orderly arrangement of their particles are called “CRYSTALLINE SOLID”. In this type of solid, the particles are arranged in layers and plane. Due to this they have definite geometric shapes e.g. Diamond, Graphite, NaCl etc are crystalline solids.

2. Amorphous Solid:

            These are the solids which do not have definite geometrical shape. The particles of such solids have a random i.e. non repetitive three dimensional arrangements. If a substance in liquid state is cooled rapidly, the particles are unable to arrange themselves in an orderly fashion, hence an amorphous solids results. Examples are glass, plastic, rubber etc.

Difference b/w Crystalline & Amorphous Solids

Crystalline Solid	Amorphous Solid
Geometry
Particles of crystalline solids are arranged in an orderly three dimensional network called crystal, hence they have definite shape.	Particles of amorphous solids are not arranged in a definite pattern, hence they do not have a definite shape.
Melting Point
Crystalline solids have sharp melting point, this is because attractive forces between particles long range and uniform.	Amorphous solids melt over a wide range of temperature i.e. they do not have sharp melting point, because the inter-molecular forces vary from place  to place
Cleavage
The breakage of a big crystal into smaller crystals of identical shape is called cleavage. Crystals cleavage along particular direction.	Amorphous solids do not break down at fixed cleavage planes.
Anisotropy & Isotropy
Physical properties of crystals such as electrical conductivity, refractive index, , are different in different direction. This property is called Anisotropy. For Example Graphite can conduct electricity parallel to its plane of layers but not perpendicular to plane.	Amorphous solids are isotropic, i.e. their physical properties are same in directions.
Symmetry
When crystalline solids, are rotated about an axis their appearance does not change i.e. they possess symmetry.	Amorphous solids are not symmetrical.

Types of Crystals:

            Crystals are classified on the basis of kind of bond, by which atoms, ions or molecules are held together in solid. They are classified into the following four types.

1) Ionic Crystals:

            Such crystals which have ionic bonds are called Ionic Crystals. In ionic crystals, there are electrostatic forces of attraction between positive and negative ions.

e.g. NaCl, KCl, BaCl₂­ etc.

Properties:

1. The ionic crystals are brittle.

2. The ionic crystals are bad conductors of electricity.

3. They have high melting point.

4. They have very high values of lattice energy.

5. They have high melting point.

2) Covalent Crystals:

            In covalent crystals the atoms or molecules are held together by covalent bonds. Non – metals usually form this type of crystals e.g. Diamond, Sic etc.

Properties:

1. They are very hard.

2. The covalent crystals have high melting points.

3. They have low coefficients of expansion.

4. They have high refractive indices.

5. They are non – conductors of electricity.

3) Molecular Crystals:

            In molecular crystals, the molecules are held together due to Vander Wall’s forces. Vander Wall’s forces result from dipole-dipole interaction.

e.g. H₂O, CO₂, NH₃ etc.

Properties:

1. Molecular crystals are soft, wax like solids.

2. They have low melting point.

3. They are non-conductor of electricity.

4. They are non-conductor of heat.

5. They are usually brittle.

4) Metallic crystals:

            In metal, valence electrons are loosely attached in a crystal and these electrons can jump to the other atoms. When one or more electrons detach themselves from an atom a positive charge on the atom is produced. Thus, free electrons serve as an atmosphere of evenly distributed negative charge and positive ions are immersed in it. Examples may be taken as Na, Cu or Fe etc.

Properties:

1. The metals are good conductor of heat and electricity.

2. They have high tensile strength.

3. They are malleable and ductile.

4. They have luster.

5. They have high lattice energies.

Isomorphism:

            When two different substances have same crystal structure, they are said to be isomorphous and the phenomenon is called Isomorphism.e.g.

K₂Cr₂O₇ & K₂SO₄ are orthorhombic.

CaCO₃ & NaNO₂ are Trigonal.

ZnSO₄ & NiSO₄ are orthorhombic.

Properties:

            Isomorphic substances have following properties:

1. They have different physical and chemical properties.

2. They have empirical formula.

3. When their solutions are mixed, they from mixed crystals.

4. They show the property of over growth.

Polymorphism:

            The substance which can exist in more than one crystalline form, under different condition, is called Polymorphous and the phenomenon is called Polymorphism. e.g. CaCO₃ exist in nature in two crystalline form

1. Calcite , which is Trigonal      2. Aragonite, which is orthorhombic

UNIT CELL:

            Unit cell is a basic structural of a crystal having a definite geometrical shape and containing a definite no. of atoms or ions. The different arrangement of these unit cells in three dimensions, give different external shape of the crystal.

CRYSTAL SYSTEM:

            These are the group of crystals whose external shapes are built up by only one kind of unit cell. A crystal unit cell is three dimensional therefore it has three axis and three angles b/w three axis. The length, breath and height a, b & c, while angle between these lengths  µ ,b and g.   The crystal are classified into a following even crystal system formed from seven types of unit cell.

1. CUBIC SYSTEM:

            In this system, all length are equal and all the angle are of 90˚. i.e.

a=b=c

& a=b=g=90˚

e.g.                  Nacl, NaBr, Diamond etc.

2-TETRAGONAL SYSTEM:

            In this system, all the length are different but the angles are equal and of 90˚.

i.e.       a=b≠ c

&         µ=b=g=90˚

e.g.      SnO₂, BaSO₄,4H₂O

3-orthorhombic SYSTEM:

            In this system, all the length are different but the angle are equal to 90˚.

i.e.       a ≠ b ≠ c

& µ=b=g=90˚

e.g.      FeSO₄.7H₂O, ZnSO₄.7H₂O etc.

4-TRIGONAL SYSTEM: (RHOMBOHEDRAL)

            In this system, all the length are equal and all the angles are equal but more than 90^o & less than 120^o i.e.

a = b = c

&

µ=b=g¹90˚ (Angles > 90^o < 120^o)

e.g. KNO₃, AgNO₃ etc.

5. Hexagonal System:

            In this systems tow lengths are equal but third length is different. Also, two angles are of 90^o but third angle is 120^o i.e.

a = b ≠ c

& µ=b =90˚

g = 120^o

            e.g.      SiO₂, Graphite etc

6. Mono clinical System:

            In this system, all the lengths are different. Two angles a^’ and g^’ are of 90^o and third angle b^’ is different.

i.e. a ≠ b ≠ c

& a = g = 90^o

b ≠ 90^o

e.g.

CuSO₄.5H₂O, Na₂CO₃.10H₂O

7. Triclinic System:

In this system, all the lengths and all the angles are different.

i.e. a ≠ b ≠ c

a ≠ b ≠ g ≠ 90^o

e.g.

CuSO₄.5H₂O, K₂Cr₂O₇ etc.