Solid State Chemistry
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Transcript of Solid State Chemistry
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