This document discusses the different types of solids and their structures. It defines crystalline and amorphous solids, with crystalline solids having a specific organized arrangement of particles and amorphous solids having a random arrangement. Crystalline solids are further divided into ionic, covalent network, molecular, and metallic crystals based on the type of bonding between particles. The document also discusses crystal lattices, unit cells, lattice parameters, crystal systems, and Bravais lattices which describe the geometric arrangements of particles in crystalline solids.

1. INTRODUCTION

2.  Solid-- Solid is one of the four fundamental states of matter. The molecules in a solid are closely
packed together and contain the least amount of kinetic energy. A solid is characterized by structural
rigidity and resistance to a force applied to the surface.
Types of Solids
On the basis of the arrangement of constituent particles, the solids are
classified into two categories, namely:
Amorphous Solids
Crystalline Solids

3.  Crystalline Solids
 The solids in which the constituent particles of matter are arranged and organized in a
specific manner are called Crystalline Solids.
 These solids contain crystals in their structure and each crystal has definite geometry.
Almost all solids fall in the category of crystalline solids including metallic elements
(iron, silver, and copper) and non-metallic elements (Phosphorus, Sulphur, and iodine).
Also several compounds like sodium chloride, zinc sulphide , diamond , graphite, iron
etc
 Amorphous Solids
 The solids in which the constituent particles of matter are arranged in a random manner
are called amorphous solids. It is a non-crystalline solid with no proper arrangement
of atoms in the solid lattice.
 In other words, we can define amorphous solids as materials which don’t have certain
organized arrangement of atoms and molecules. One of the most common examples of
amorphous solids is glass, which is used widely in the manufacturing sector .

4.  Classes of Crystalline Solids
 Crystalline substances can be described by the types of particles in them and the types
of chemical bonding that takes place between the particles. There are four types of
crystals: (1) ionic, (2) molecular , (3) covalent network, and (4) metallic crystal
 Ionic crystals -- The ionic crystal structure consists of alternating positively-charged
cations and negatively-charged anions. Ionic crystals are hard and brittle and have high
melting points. Ionic compounds do not conduct electricity as solids, but do conduct
when molten or in aqueous solution.ex-NaCl, CaF2 etc
 Covalent network crystals -- A covalent network crystal consists of atoms at the
lattice points of the crystal, with each atom being covalently bonded to its nearest
neighbor atoms . Ex- diamond, quartz
 Molecular crystals -- Molecular crystals typically consist of molecules at the lattice
points of the crystal, held together by relatively weak intermolecular .Some molecular
crystals, such as ice,

5. Metallic crystal -- Metallic crystals consist of metal cations surrounded by a “sea” of
mobile valence electrons (see figure below). These electrons, also referred to as
delocalized electrons, do not belong to any one atom, but are capable of moving through
the entire crystal. As a result, metals are good conductors of electricity. Ex- Al, Fe ,Cr ,Ni
etc
 Structure of some of the more important metallic
crystals are-
 Face centered cubic structure(fcc) –Cu , Al ,Ag etc
 Body centered cubic structure(bcc) – W , Mo ,Cr etc
 Hexagonal closed packed structure(hcp) –Mg ,Zn, Ti ,Cd etc
metallic crystal have wide use in engineering owing to
 Their favourable properties of strength , ductility ,
Conductivity etc

6. Crystalline solids Amorphous solids
The constituent particles are arranged in a
regular fashion
The constituent particles are not arranged in any
regular fashion
They have definite geometric shapes They have irregular shapes
Intermolecular forces between atoms are equal
Intermolecular forces between atoms are not
equal
It posses short range order as well as long range
order
It posses short range order
They have sharp melting points They melt over a range of temperature
They are anisotropic They are isotropic
They have definite heat of fusion They do not have definite heat of fusion
They undergo a clean cleavage when cut with
knife
They undergo an unclean cleavage when cut with
knife
They are true solids They are pseudo solids or supercooled liquids
Example- quartz , diamond, iron , copper etc
Example-Silica glass is amorphous SiO2 , rubber ,
plastic etc

7. CRYSTAL LATTICE
 Crystal lattice is the three dimensional arrangements of constituent particles (atoms, molecules,
ions) of crystalline solids as points. Or the geometric arrangement of constituent particles of
crystalline solids as point in space is called crystal lattice.
characteristicsss of crystal lattice:
 Each constituent particle is represented by one point in a crystal lattice.
 These points are known as lattice point or lattice site.
 Lattice points in a crystal lattice are joined together by straight lines.
 By joining the lattice points with straight lines the geometry of the crystal lattice is formed.

8. UNIT CELL
Unit Cell: The smallest portion of a crystal lattice is called Unit Cell. By
repeating in different directions unit cell generates the entire lattice.

9. LATTICE PARAMETER
A unit cell is characterized by six parameters. These parameters are three
edges (a, b and c) and angles between them (α, β and γ).
Dimensions along the edges of a unit cell is represented by a, b and c.
Edges of unit cell may or may not be mutually perpendicular.
The angle between b and c is represented by α, between a and c by β and
between a and b by γ.

10. Types of Unit Cell: There are two types of unit cells – Primitive and non
primitive unit cell
 Primitive Unit Cells: When particles in unit cell are present only at the corners, it is
called the primitive unit cell.
 non primitive Unit Cells: When particles are present at other positions in addition to
those at corners in a unit cell, it is called a Centred Unit Cell.

11. CRYSTAL SYSTEM
Crystal system is a method of classifying crystalline substance on
the basis of their unit cell.
They differ in their lattice parameters
There are 7 basic crystal systems

13. BRAVIAS LATTICE
 There are 14 bravias lattice, that means there are only 14 independent ways of
arranging points in 3 –dimensions in a crystal lattice to describe all possible
arrangements of points in space.