Solid State

SOLIDS

Substances having definite shape and definite volume.

E.g.stone,sand,chair,pen etc.

Characteristics:Solids

1.They have definite shape and volume.

2.They are almost incompressible.

3.They have high densities.

4.They possess strong inter molecular forces of attraction.

5.Their particles have fixed positions.

6.Their particles undergo vibratory motion only.

7.They are rigid.

CLASSIFICATION OF SOLIDS

On the basis of arrangement of particles solids are of two types :

1. Crystalline Solids

These Solids have regular arrangement of particles in three dimensional space.

E.g. quartz,diamond,graphite etc.

2. Amorphous Solids

These Solids have irregular arrangement of particles in three dimensional space.

E.g. plastic,rubber,glass,pitch etc.

CHARACTERISTICS:CRYSTALLINE SOLIDS

1.They have regular arrangement of particles.

2.They are anisotropic.

3.They have long range order.

4.They have sharp melting points.

5.They have definite regular geometry.

6.They are true solids.

7.E.g. quartz,diamond,graphite,NaCl etc.

CHARACTERISTICS:AMORPHOUS SOLIDS

1.They have irregular arrangement of particles.

2.They are isotropic.

3.They have short range order.

4.They have melt over a range of temperature.

5. They don't have regular geometry.

6. They are pseudo solids or super cooled liquids.

7.E.g. plastic,rubber,glass,pitch etc.

Difference b/w crystalline and amorphous solids
CRYSTALLINE SOLIDS	CRYSTALLINE SOLIDS
1.They have regular arrangement of particles.	1.They have irregular arrangement of particles.
2.They are anisotropic.	2.They are isotropic.
3.They have long range order.	3.They have short range order.
4.They have sharp melting points.	4.They have melt over a range of temperature.
5.They have definite regular geometry.	5.They don't have regular geometry.
6.They are true solids.	6.They are pseudo solids or super cooled liquids.
7.E.g.quartz,diamond,graphite,NaCl etc.	7.E.g.plastic,rubber,glass,pitch etc.

TYPES OF CRYSTALLINE SOLIDS

On the basis of types of particles and nature of binding forces they are of four types:

1. Ionic Solids

In these solids the constituent particles are ions which are held together by ionic bond. E.g. NaCl,CsCl etc.

2. Molecular Solids

In these solids the constituent particles are molecules which are held together by weak Vander Waal's forces.E.g.Solid Carbon dioxide,Iodine,Ice,Naphthalene etc.

3. Covalent Solids

In these solids the constituent particles are atoms which are held together by covalent bond. E.g. Quartz,Diamond,Graphite etc.

4. Metallic Solids

In these solids the constituent particles are positively charged kernels and mobile electrons.These particles are held together by metallic bonds.E.g.Fe,Au etc.

IMPORTANT QUESTIONS

Q: How does Amorphous Silica differ from quartz ? OR
Q:- Differentiate between Quartz and Quartz glass . OR
Q:-Quartz is a Crystalline solid whereas glass is an Amorphous solid.Why? OR
Q:-Quartz is a Crystalline form of silica whereas Glass is an amorphous form of Silica. Why?

Ans:-In case of quartz the silicate tetrahedral units (SiO4) have regular arrangement whereas in glass the silicate tetrahedral units have irregular arrangement.Hence quartz is a crystalline solid whereas glass is an amorphous solid.

Q:- Glass is called pseudo solid or super cooled liquid .Why?

Ans: - Glass is called pseudo solid because it flows like liquid. Moreover it is obtained when molten silica is cooled rapidly hence it is also called super cooled liquid.

Q: - Amorphous solids are called pseudo solids or super cooled liquids why?

Ans: - They are called pseudo solids because they have the tendency to flow like liquids moreover they are made by rapidly cooling the molten material hence they are also called super cooled liquids.

Q: - What is annealing?
Ans: - Any material can be made amorphous by rapidly cooling its melt. This is called annealing .E.g. when molten silica is cooled rapidly it forms glass which is an amorphous form of silica.

Q: - What are crystallites?

Ans: - The crystalline parts present in the amorphous solids are called crystallites. These crystallites occur in amorphous solids due to their short range order.

Q: - What is isotropy?

Ans: - In amorphous solids the physical properties like electrical conductivity, thermal conductivity etc, have same values in all the directions. These solids are called isotropic and the process is known as isotropy.

Q: - What is anisotropy?

Ans: - In crystalline solids the physical properties like electrical conductivity, thermal conductivity etc, have different values in different directions within the same crystal. These solids are called anisotropic and the process is known as anisotropy.

CRYSTAL

It is a solid object having definite geometrical shape, flat faces and sharp edges. crystals

CRYSTAL LATTICE

The regular arrangement of particles of a crystalline solid in three dimensional space is called crystal lattice or space lattice. lattice

LATTICE POINTS

The points occupied by the particles in the crystal lattice are called lattice points or lattice sites .

INTERSTITIAL SITES

The vacant spaces present in between the particles in the crystal lattice are called lattice interstitial sites.

UNIT CELL

The smallest repeating unit which when repeated again and again produces the complete crystal lattice.

TYPES OF UNIT CELL

1) Primitive or simple unit cell

The unit cells in which particles are present only at the corners are called primitive or simple unit cells. E.g. Simple cubic unit cell etc.

2)NON-PRIMITIVE UNIT CELL

The unit cells in which particles are present not only at the corners but also at some other positions within the unit cell are called non-primitive unit cells or centered unit cells. E.g. fcc and bcc.

TYPES:NON-PRIMITIVE UNIT CELLS

i) Face centered unit cell

The unit cell in which particles are present at all the corners as well as at the center of each face is known as face centered unit cell. E.g. face centered cubic unit cell.

ii) Body centered unit cell

The unit cell in which particles are present at all the corners as well as in the center of the body is known as body centered unit cell. E.g. body centered cubic unit cell.

iii) End centered unit cell

The unit cell in which particles are present at the corners as well as at the centers of any two opposite faces is known as end centered or end- face centered unit cell. E.g. End centered monoclinic unit cell.

OUTLINE :TYPES OF UNIT CELLS

TYPES:CUBIC UNIT CELL

1.Simple or primitive

The unit cell in which particles are present at all the corners is called simple cubic unit cell.

2.Body centered

The unit cell in which particles are present at all the corners as well as in the center of the body is known as body centered cubic unit cell

3.Face centered

The unit cell in which particles are present at all the corners as well as at the center of each face is known as face centered cubic unit cell.

CRYSTAL SYSTEMS

There are present seven crystal systems .They are also known as seven crystal habits. Out of these seven crystal systems the cubic crystal system is the most symmetrical whereas triclinic is the least symmetrical.There are 14 different types of space lattices in all these seven systems. These are called 14 Bravais lattices.

CALCULATION:ATOMS IN CELLS

For more clarity look at the image below showing cut out sections of atoms per unit cell

DENSITY (P) OF CUBIC UNIT CELLS

NUMERICAL ON DENSITY OF CUBIC CRYSTAL LATTICE

(1)An element Cr has bcc structure with edge length 288pm.The atomic mass of chromium is 51.78.Calculate density.[Ans:7.22g/cm3]

2)An element has fcc structure with edge length 200 pm .200 g of this element contains 24 × 1023 atoms.[Ans:41.7g/cm3]

(3)An element with atomic mass 60 has fcc structure with edge length 400 pm. Calculate density.[Ans:6.23g/cm3]

(4)The edge length of NaCl is 564 pm .calculate density. Atomic mass of sodium is 23 g/mol and that of chlorine is 35.5 g/mol.[Ans:2.16g/cm3]

(5) The compound CuCl has ZnS structure (fcc) and the edge length of its unit cell is 500 pm. Calculate its density.(Atomic mass Cu = 60 gm/mol and Cl = 35.5 g/mol.) [Ans :- 5.23 g/cm3]

CHECK YOUR CONCEPTS

Q: - How many types of crystal systems are there write their names?

Q: - How many types of unit cells are there in cubic crystal system? Write their names.

Q: - Write down formula to calculate density of the unit cells.

Q: - How many atoms are there in bcc and fcc?

Q: - How many faces edges and corners a cube has?

Q:-Calculate the number of atoms in all the three cubic unit cells.

Q: - Define simple cubic unit cell, bcc and fcc with diagrams.

Q:-Give four examples of amorphous solids

NUMERICAL of a, d AND r

Q :-Gold has fcc arrangement with atomic radius 0.414 nm.calculate edge length.(under root 2=1.414)
Ans: - a = 1.17 nm

Q: - CsCl has bcc arrangement with edge length 400 pm.Calculate nearest neighbor distance. (Under root 3=1.732).
Ans :- d = 346.4 pm

Q :- The radius of an atom is 220 pm. It has fcc structure .calculate edge length.
Ans :- a = 622.16 pm

Q :- Xenon has fcc lattice. Edge length of unit cell is 620 pm. Calculate d and r of xenon.
Ans ;- d = 438.5 pm ; r = 219.5 pm

Q :- CsCl has bcc lattice.Cs+ and Cl- are diagonally connected. Edge length is 412 pm .radius of Cl- ion is 181 pm.Calculate the radius of Cs+ ion.
Ans : hint (apply nearest neighbor distance formula)
d is also = rCs+ and rCl- ; (Ans :rCs+ = 175.8 pm)

DERIVATION OF FORMULA FOR a,d and r

1. FOR SIMPLE CUBIC UNIT CELL:

d = AB = a
d = a
r = AB/2 = a/2
a = 2r

COORDINATION NUMBER

The number of spheres touching to a given sphere is known as coordination number.E.g. Consider the following to arrangements.

Q: - What is the effect of temperature and pressure on the coordination number of solids ?

Ans: - With the increase in temperature coordination number decreases whereas with the increase in pressure the coordination number increases

INTERSTITIAL SITES

The vacant spaces present in the crystal are called interstitial sites.These are also called voids or holes.

TYPES OF VOIDS: TWO TYPES

(1)TETRAHEDRAL VOID

The vacant triangular space tetrahedrally surrounded by four spheres is called tetrahedral void.

(2)OCTAHEDRAL VOID

The double triangular vacant space octahedrally surrounded by six spheres is called octahedral void.

RADIUS RATIO

The ratio of radius of cation to that of anion .

Radius ratio = r+/r-

RADIUS RATIO RULE

The relationship among radius ratio, coordination number and geometry is called radius ratio rule.

NUMERICAL :RADIUS RATIO

(1)The radius of Na+ is 95 pm and Cl- is 181 pm.Calculate radius ratio and predict the coordination number and geometry.Ans: = 0.524

(2)The two ions A+ and B- have radii 88 pm and 200 pm. Calculate radius ratio and predict the coordination number and geometry.

(3)The radii of cation and anion are 82 pm and 195 pm respectively. Calculate radius ratio and predict the coordination number and geometry.

CLOSE PACKING IN SOLIDS

The packing in which maximum space is occupied is called close packing.

TYPES CLOSE PACKING:

(1)Close packing in one dimension.

In this packing the spheres are arranged in a linear manner in a row. The coordination number of this arrangement is 2.

(2)Close packing in two dimensions.

It is of two types.

(1)SQUARE CLOSE PACKING

When we place the spheres of the second row exactly below the spheres of the first row and this pattern is repeated ,we get square close packing .coordination number is 4.The packing efficiency is 52.4%.

(2)Hexagonal close packing

This packing is obtained when we place the spheres of the second row in the depressions of the first row and this pattern is repeated. The coordination number is 6 and the packing efficiency is 60.4 %.

(3)Close packing in three dimensions.

This packing is obtained by extending the two dimensional close pickings into three dimensions. It can be divided into four parts.

(1)Simple cubic close packing

This packing is obtained from square close packing in two dimensions .Here we place the spheres of the second layer exactly above the spheres of the first layer. The coordination number is 6 and packing efficiency is 52.4 % .

(2)Body centered cubic close packing

This close packing is obtained from two dimensional square close packing by keeping the spheres of the first layer a little apart and then placing the spheres of the second layer on the holes of the first layer. This pattern is repeated .The coordination number is 8 .packing efficiency is 68 % .

(3)Face centered cubic close packing.

This arrangement is obtained from hexagonal close packing in two dimensions. We place the spheres of the second layer on the depressions of the first layer .In the second layer we get two types of holes tetrahedral holes and octahedral holes. When we place the spheres of the third layer on the octahedral holes of second layer, we get face centered cubic close packing. This packing is also known as ABCABC…type. The coordination number is 12 and packing efficiency is 74 %.

(4)Hexagonal close packing in three dimensions

This arrangement is obtained from hexagonal close packing in two dimensions. We place the spheres of the second layer on the depressions of the first layer .In the second layer we get two types of holes tetrahedral holes and octahedral holes. When we place the spheres of the third layer on the tetrahedral holes of second layer, we get hcp in three dimensions. This packing is also known as ABAB…type. The coordination number is 12 and packing efficiency is 74 %.

PACKING EFFICIENCY

It is defined as the percentage of total space occupied by the solid particles.

Square close packing: The packing efficiency is 52.4%.

Hexagonal close packingin 2 dimensions packing efficiency is 60.4 %.

Simple cubic close packing: packing efficiency is 52.4 %

Body centered cubic close packing:packing efficiency is 68 %

Face centered cubic close packing:packing efficiency is 74 %

Hexagonal close packing in three dimensions: packing efficiency is 74 %.

PACKING EFFICIENCY IN CLOSE PACKINGS
CLOSE PACKING	PACKING EFFICIENCY
1Square close packing.	packing efficiency:52.4%.
2.Hexagonal close packing in 2 dimensions.	packing efficiency:60.4 %.
3.Simple cubic close packing.	packing efficiency:52.4 %.
4.Body centered cubic close packing.	packing efficiency:68 %.
5.Face centered cubic close packing.	packing efficiency: 74 %.
6.Hexagonal close packing in three dimensions.	packing efficiency:74 %.