Solid State ChemistrySolid State ChemistryPart 1Part 1

Dr. S. UnnikrishnanGeneral Manager R&D

IPCL, Vadodara

State of Matter• Definite Volume• Definite shape

Kinetic Molecular model• Regular order of constituent particles• Strong inter-particle forces• Fixed spatial position for constituent particles• Properties dependant on constituents and nature of arrangement

The Solid StateThe Solid State

Classification of Classification of SolidsSolids

Molecular solidsConstituent particles : molecular particlesVan der Waals type inter-particle forces (weak)e.g. : Solid Carbon dioxide, Ice, Iodine, Naphthalene, Camphor

Ionic SolidsConstituent particles : + vely and - vely charged ions, arranged in regular fashion throughout the crystal Strong electrostatic inter-particle forces

e.g. : NaCl, NaNO3, LiF, Na2SO4, KI

Classification of SolidsClassification of Solids ….….

Covalent SolidsConstituent particles: Atoms held together by covalent bondse.g. : SiO2, SiC, Diamond

Metallic solidsConstituent particles: Positive kernels immersed in a sea of mobile electrons Metallic bonds between the constituentse.g. : Cu, Ni, Fe, Au, Ag

Space Lattice & Unit Space Lattice & Unit cellcell

Lattice : “Regular array of points in 1,2 or 3 dimensions.”

Crystalline solids: Regular 3-D array of constituent particles

Space Lattice : “ A regular arrangement of the constituent

particles (atoms/ions/molecules) of a crystalline solid in 3-D

space.”

Lattice Points/Sites : “Positions which are occupied by

atoms, ions or molecules in the crystal lattice.”

Unit Cells : “The smallest repeating unit arranged in regular

3-D and forming the space lattice.”

a

b c

Simple cubic unit cell

3-D Array of simple cubes forming a lattice

Packing in Packing in SolidsSolids

Close packing: •To achieve maximum space occupancy•High density of packing•Higher stability

Close packing in 2- Dimension1. Square packing2. Hexagonal packing

Coordination number“The number of spheres touching (or being in contact with) a given sphere in a close packed array”For square packing the C.N. is 4For hexagonal packing the C.N. is 6

Tetragonal void

Square layer arrangement

Square layer arrangement is called so because on joining the centre of the nearest neighbours

of any sphere, a square is formed.

Square layer arrangement

Hexagonal layer arrangement

Trigonal void

Hexagonal layer arrangement is called so because on joining the centre of the

nearest neighbours of any sphere, a regular hexagon is formed.

Hexagonal layer arrangement

3-D stacking of Hexagonal Array

First layer

Second layer

Octahedral site formation

Shape obtained by joining the centres of

the surrounding spheres (octahedron)

Tetrahedral site formation

Shape obtained by joining the centres of

the surrounding spheres (tetrahedron)

T-void

O-voids

The third layer can be placed in two different ways.

Overhead view:

TO

O

O

T-void

O-voids

Covering t-voids:Overhead view:

TO

O

O

Covering t-voids:

Unit cell of hexagonal closed

packed arrangement.

TO

O

O

Overhead view:

Covering o-voids:

O-void

TO

O

O

Overhead view:

Covering o-voids:

TO

O

O

Overhead view:

Covering o-voids:

Now the fourth layer can be placed in only one way- by covering o-voids; hence being similar to the first layer.

Cubic closed packed/ face centred closed packed structure.

O

O

O

Overhead view:

O

SC

FCC

BCC

A corner is shared by 8 cubesA face is shared by 2 cubesAn edge is shared by 4 cubesA body centre is exclusive

A sphere located at the body centre of the unit cell belongs solely to it.

A sphere located at the face centre belongs to two unit cells.

A sphere located at the edge belongs to four unit cells.

A sphere located at the corner belongs to eight unit cells.

Simple cubic: Constituent particles occupy corners of a cube.

Types of cubic unit cells

Body centred cubic: Constituent particles occupy corners of a cube and the body centre.

Types of cubic unit cells

Face-centred cubic: Constituent particles occupy corners of a cube and face centres.

Types of cubic unit cells

sodium ion

Chloride ion

FCC arrangement of Na+ and Cl-

interpenetrated into each other.

NaCl crystal structure

The ZnS Structure

Zn2+

S2-

S2- forms a FCC orderZn2+ occupy 4 Tetrahedralsites

4 S2- ions per unit cell4 Zn2+ ions per unit cell

The CsCl structure

Cs+ ion

Cl- ion

Cs+ ion surrounded by 8 Cl- ions in cubic coordinationCl- ion surrounded by 8 Cs+

ions in cubic coordination

The CaFThe CaF22 StructureStructure

F- ion

Ca2+ ion

•Ca+ ions form the FCC•F- ions occupy the Tetrahedral sites

4 Ca2+ ions per unit cell8 F- ions per unit cell

Cation

Anion

Cation displaced to interstitium.

Frenkel defectFrenkel defect

Cation

Anion

Cationic vacancy.

Anionic vacancy.

Schottky defectSchottky defect

Density - Number of atoms/unit cell - unit Density - Number of atoms/unit cell - unit cell edgecell edge

Unit cell edge ‘a’ , No. of atoms in unit cell ‘Z’, Atomic mass of the element ‘M’

Volume of the cubic unit cell ‘V’ = (a3) (1)

Density of unit cell ‘Dunit cell ‘ = Mass of unit cell ‘Munit cell’ / V (2)

Mass of unit cell = No. of atoms per unit cell x mass of each atom

i.e. Munit cell = Z x m where m is the mass of each atom

Mass of each atom ‘m ‘ = atomic mass ‘M’ / Avogadro Number ‘N0’

i.e. m = M / N0

Hence, Mass of unit cell Munit cell = Z x M/ N0 (3)

Substituting (1) and (3) in (2), we get

Density D = (Z.M/ N0) / a3

i.e. Density of the material (or of the unit cell) D = Z.M / N0 . a3

Packing in Oxides of Packing in Oxides of IronIronIron oxides: Ferrous oxide (FeO), Ferric oxide (Fe2O3) and

Magnetite (Fe3O4)

FeO : Forms NaCl structure with O2- forming FCC and Fe2+

occupy octahedral sites, ideally. (Fe0.95O)

Fe2O3 : Corrundum structure!

Fe3O4 : Forms Inverse spinel structure

Inverse Spinel: O2- form FCC structure, Fe2+ and Fe3+ occupy O and T

sites as shown : (Fe3+)T {Fe2+, Fe3+}O O4

Examples : Fe3O4, MgFe2O4

Normal Spinel: O2- form the FCC assembly, the M2+ and M3+ occupy

the O and T sites as shown: (M2+)T {Fe23+} O4

Examples: Mg Al2O4, Zn Fe2O4