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.

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

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

Some Simple Ionic Compounds
NaCl has a fcc structure.

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.