Revision Notes on Solid State

S.No.

Crystalline Solids

Amorphous solids

1

Regular internal arrangement  of particles

irregular internal arrangement  of particles

2

Sharp melting point

Melt over a rage of temperature

3

Regarded as true solids

Regarded as super cooled liquids or pseudo solids

4

Undergo regular cut  

Undergo irregular cut.

5

Anisotropic in nature

Isotropic in nature

Crystal  Classification 

Unit Particles 

Binding Forces 

Properties 

Examples 

Atomic

Atoms

London dispersion forces

Soft, very low melting, poor thermal and electrical conductors

Noble gases

Molecular

Polar or 
non – polar molecules

Vander Waal’s forces (London dispersion, dipole – dipole forces hydrogen bonds)

Fairly soft, low to moderately high melting points, poor thermal and electrical conductors

Dry ice (solid, methane

Ionic

Positive and negative ions

Ionic bonds

Hard and brittle, high melting points, high heats of fusion, poor thermal and electrical conductors

NaCl, ZnS

Covalent

Atoms that are connected in covalent bond network

Covalent bonds

Very hard, very high melting points, poor thermal and electrical conductors

Diamond, quartz, silicon

Metallic Solids

Cations in electron cloud

Metallic bonds

Soft to very hard, low to very high melting points, excellent thermal and electrical conductors, malleable and ductile

All metallic elements, for example, Cu, Fe, Zn

Crystal Systems

Bravais Lattices 

Intercepts 

Crystal angle 

Example

Cubic 

Primitive, Face Centered, Body Centered 

a = b = c

a = b = g = 90^o 

Pb,Hg,Ag,Au Diamond, NaCl, ZnS 

Orthorhombic

Primitive, Face Centered, Body Centered, End Centered

a ≠ b ≠ c

a = b = g = 90^o

KNO₂, K₂SO₄

Tetragonal

Primitive, Body Centered

a = b ≠ c

a = b = g = 90^o

TiO₂,SnO₂

Monoclinic

Primitive, End Centered

a ≠ b ≠ c

a = g = 90^o, b≠ 90^o

CaSO₄,2H₂O

Triclinic

Primitive

a ≠ b ≠ c

a≠b≠g≠90⁰

K₂Cr₂O₇, CaSO₄5H₂O

Hexagonal

Primitive

a = b ≠ c

a = b = 90⁰, g = 120^o

Mg, SiO₂, Zn, Cd

Rhombohedra

Primitive

a = b = c

a = g = 90^o, b≠ 90^o

As, Sb, Bi, CaCO₃ 

Close structure

Number of atoms per unit cell ‘z’.

Relation between edge length ‘a’ and radius of atom ‘r’

Packing Efficiency

hcp and ccp or fcc

4

r = a/(2√2)

74%

bcc

2

r = (√3/4)a

68%

Simple cubic lattice

1

r = a/2

52.4%

Coordination numbers

Geometry

Radius ratio (x)

Example

2

Linear

x < 0.155

BeF₂

3

Planar Triangle

0.155 ≤ x < 0.225

AlCl₃

4

Tetrahedron

0.225 ≤ x < 0.414

ZnS

4

Square planar

0.414 ≤ x < 0.732

PtCl₄^2-

6

Octahedron

0.414 ≤ x < 0.732

NaCl

8

Body centered cubic

0.732 ≤ x < 0.999

CsCl

Structures

Descriptions

Examples

Rock Salt Structure

Anion(Cl^-) forms fcc units and cation(Na⁺) occupy octahedral voids. Z=4 Coordination number =6

NaCl, KCl, LiCl, RbCl

Zinc Blende Structure

Anion (S^2-) forms fcc units and cation (Zn²⁺) occupy alternate tetrahedral voids Z=4 Coordination number =4

ZnS _, BeO

Fluorite Structures

Cation (Ca²⁺) forms fcc units and anions (F^-) occupy tetrahedral voids Z= 4 Coordination number of anion = 4 Coordination number of cation = 8

CaF₂, UO₂, and ThO₂

Anti- Fluorite Structures

Oxide ions are face centered and metal ions occupy  all the tetrahedral voids.

Na₂O, K₂O and Rb₂O.

Cesium Halide Structure

Halide  ions are primitive cubic while the metal ion occupies the center of the unit cell.
Z=2
Coordination number of = 8

All Halides of Cesium.

Pervoskite Structure

 One of the cation is bivalent and the other is tetravalent. The bivalent ions are present in primitive cubic lattice with oxide ions on the centers of all the six square faces. The tetravalent cation is in the center of the unit cell occupying octahedral void.

CaTiO₃, BaTiO₃

Spinel and Inverse Spinel Structure

Spinel :M²⁺M₂³⁺O₄, where M²⁺ is present in one-eighth of tetrahedral voids in a FCC lattice of oxide ions and M³⁺ ions are present in half of the octahedral voids. M²⁺ is usually Mg, Fe, Co, Ni, Zn and Mn;  M³⁺ is generally Al, Fe, Mn, Cr and Rh.

MgAl₂O_{4 ,} ZnAl₂O₄, Fe₃O₄,FeCr₂O₄ etc.