Solid State

The most important distinguishing characteristic of solids is that they are rigid and tightly bound .Solids have a fixed shape and volume . Solids have the highest intermolecular force of attraction , due to which they have high melting and boiling points . Atoms in a solid possess vibrational motion . The particles cannot move much due to close packing ; so the particles vibrate about their mean positions . Solids have the least thermal and kinetic energy , due to lack of motion of individual particles .

There are two types if solids :- 1) Crystalline 2) Amorphous

## Crystalline Solids

Crystalline Solids are homogeneous solids and have a fixed , repetitive arrangement of atoms . These solids have a fixed melting point. Crystalline solids show anisotropy . The repetitive crystals are called as a unit cell and the entire structure is called as crystal lattice .

## Amorphous Solids

The substances that appear like solids but do not have well ordered crystalline structure are called as Amorphous Solids . Amorphous solids do not have a fixed , repetitive arrangement of atoms . These are also known of pseudo solids or supercooled liquids . e.g. glass . These solids melt over a range of temperatures , i.e. they don't have a fixed melting point . Amorphous solids may show anisotropy or isotropy. Their range of repitition is very short.

## Properties of Solids

**Anisotropy :** Anisotropy is the property of solids to change their physical properties with change in direction .

**Isomorphous Solids :** Isomorphous Solids are the solids having the same structure .

**Polymorphous Solids :** Polymorphous solids have two or more structures .

**Allotropy :** Allotropes are two solids having different structures but same chemical propeties .

## Types of Crystalline Solids

### **Molecular Solids**

The constituent particles are molecules . Based on the type of molecules , these are classified into 3 types .

particles
molecules
molecules
 Interaction
Dipole
 Dipole Moment
 M.P. / B.P

Molecular Solids are generally soft .

### **Ionic Solids**

The constituent particles are ions . All salts are crystalline in nature and are called as ionic solids . The arrangement of atoms depends on the following 3 factors :-

1)Size of the cation & Anion

2)Charges on the Ions

3)The ease with which the ion can be polarized .

### **Metallic Solids**

The constituent particles are metal atoms . The atoms are bound together by metallic bonds , i.e. between cations and free electrons . On application of shear force , these solids do not get fractured but break apart smoothly .

### **Covalent Solids**

Covalent solids are also called as giant solids .
The constituent particles are non-metallic atoms . Covalent solids are formed by covalent bonds between the neighbouring constituent atoms of non-metallic solids .

## Bravais Lattices

A unit cell is the smallest repeating structural unit of a cell . The arrangement of atoms in unit cell is called as Bravais Lattices .

## Packing Efficiency & Density of Solids

 bcc
 fcc
& hcc

###

## Packing Configuration

### Linear Packing

Under linear packing , the atoms are arranged in a line .

### 2D Packing

**AAAA**

**ABAB**

### 3D Packing

**AAAA**

**ABAB**

**ABCABC**

## Packing in Voids

**For Ionic Solids**

The ratio of cationic radius to anionic ratio is calculated and then inference is made based on the table given below .

of Cation
 4
 6
 8

For fcc , 2(r+ + r-) = edge length

## Defects

**Point Defect :** Irregularity caused due to removal or addition of atoms , ions , molecules or impurities to the crystal lattice .

**Line Defect :**  Irregularity caused in an entire row or column of atoms .

**Types of Point Defects**

**a) Vacancy Defect :** Irregularity caused due to removal of an atom , molecule or ion from its crystal lattice .

**b) Interstitial Defect :** Irregularity caused due to the addition of an atom , molecule or ion in the crystal lattice

**c) Impurity Defect :** Irregularity caused due to the addition of impurity or an atom other than the constituent atoms , in the crystal lattice

**Non Stoichiometry Defects :**

a) Metal Excess Defect

b) Metal Deficiency Defect

## Electrical Properties

Metallic solids conduct electricity with less amount of energy , because their valence band and conduction bands overlap . Semiconductor Solids like Silicon , Germanium conduct electricity after being doped .

For better overview of this topic , Check Semiconductors

## Magnetic Properties

**Diamagnetism :** 1) All the orbitals are completely filled .

2) The spins are paired and the magnetic field is repelled .

**Paramagnetism :** 1) Atom contains unpaired electron ; i.e. their orbitals are not completely filled .

2) The spins do not cancel each other and the magnetic field is attracted .

**Ferromagnetism :** 1) Atom contains a large number of unpaired electrons .