7. WHAT IS SOLID?
• Definite shape.
• Definite volume.
• Highly incompressible.
• Rigid.
• Constituent particles held closely by strong
intermolecular forces.
• Fixed position of constituents.
8. TYPES OF SOLIDS
Two types (based upon atomic arrangement,
binding energy, physical & chemical
properties):
1.Crystalline
2. Amorphous
9. CRYSTALLInE SOLIDS
• The building constituents arrange themselves in regular
manner throughout the entire three dimensional network.
• Existence of crystalline lattice.
• A crystalline lattice is a solid figure which has a definite
geometrical shape, with flat faces and sharp edges.
• Incompressible orderly arranged units.
• Definite sharp melting point.
• Anisotropy.
• Definite geometry.
• Give x-ray diffraction bands.
• Examples: NaCl, CsCl, etc.
10. AMORPHOUS SOLIDS
• Derived from Greek word ‘Omorphe’ meaning
shapeless.
• No regular but haphazard arrangement of atoms or
molecules.
• Also considered as non-crystalline solids or super-
cooled liquids.
• No sharp m.p.
• Isotropic.
• No definite geometrical shape.
• Do not give x-ray diffraction bands.
• Examples: glass, rubber, plastics.
12. IOnIC CRYSTALS
• Lattice points are occupied by positive and negative ions.
• Hard and brittle solids.
• High m.p. due to very strong electrostatic forces of
attraction.
• Poor conductors of electricity in solid state but good in
molten state.
• Packing of spheres depends upon:
presence of charged species present.
difference in the size of anions and cations.
• Two types:
AB types.
AB2 types.
13. COvALEnT CRYSTALS
• Lattice points are occupied by neutral atoms.
• Atoms are held together by covalent bonds
• Hard solids.
• High m.p.
• Poor conductors of electricity.
• Two common examples: diamond & graphite.
14. MOLECULAR CRYSTALS
• Lattice points are occupied by neutral molecules.
• The molecules are held together by vander
Waal’s forces.
• Very soft solids.
• Low m.p.
• Poor conductors of electricity.
15. METALLIC CRYSTALS
• Lattice points are occupied by positive metal ions
surrounded by a sea of mobile e-.
• Soft to very hard.
• Metals have high tensile strength.
• Good conductors of electricity.
• Malleable and ductile.
• Bonding electrons in metals remain delocalized over
the entire crystal.
• High density.
16. LAWS OF SYMMETRY
• Plane of symmetry
• Centre of symmetry
• Axis of symmetry.
17. ELEMEnTS OF SYMMETRY
In CUbIC CRYSTAL
• Rectangular planes of symmetry: 3
• Diagonal planes of symmetry: 6
• Axes of four-fold symmetry: 3
• Axes of three-fold symmetry: 4
• Axes of two-fold symmetry: 6
• Centre of symmetry: 1
Total symmetry elements: 23
24. number of atoms Per unit
cell in a cubic lattice
• Simple cubic cell: 1atom/unit cell of sc
• Body-centered cell: 2 atoms/unit cell of bcc
• Face-centered cell: 4 atoms/unit cell of fcc
• End face-centered cell: 2 atoms/unit cell
34. atomic radius of a cubic lattice
• Simple cubic cell:
r = a/2
• Face-centered cubic cell:
r = a/√8
• Body-centered cubic cell:
r = √3a/4
(where a → length of cube)
35. Radius Ratio Rule
• Relation between the radius, co-ordination
number and the structural arrangement of the
molecule.
Radius ratio =
• Greater the radius ratio, larger the size of the
cation and hence the co-ordination number.
• density = (z*Ma)/Na*a^3 Ma=mass no.,
Na=avogadro, a= side length, z=no. of atoms
36. stRuctuRal analysis by
Radius Ratio Rule
S.NO. RADIUS CO-ORDINATION SHAPE EXAMPLE
RATIO NUMBER
1. 0.0 – 0.155 2 Linear HF-
2. 0.155–0.225 3 Triangular B2O3, BN
planar
3. 0.225– 0.414 4 Tetrahedral ZnS, SiO4-4
4. 0.414– 0.732 6 Octahedral NaCl
5. 0.732 – 1.0 8 Body-centered CsCl
cubic
37. bRaVais lattices
• Unit cell parameters:
Lengths a, b & c.
Angles α, β & γ.
• Total crystal lattices: 7
• Total Bravais lattices: 14
38. cRystal systems with unit
cell paRameteRs
S.No. System Cell Crystal Bravais Min. Sym.
Dimensions Angles Lattices Elements
1. Cubic a=b=c α=β=γ=90ْ sc, fcc, 3-fold axes: 4
bcc = 3 4-fold axes: 3
2. Orthorhombic a≠b≠c α=β=γ=90ْ sc, fcc, 2-fold axes: 3
bcc, efcc
=4
3. Tetragonal a=b≠c α=β=γ=90ْ sc, bcc= 2 4-fold axis: 1
48. stRuctuRes of impoRtant
ionic compounds
1. AB type: NaCl (rock salt)
CsCl
ZnS (zinc blende / sphalerite)
2. AB2 type: CaF2 (fluorite)
TiO2 (rutile)
SiO2
49. Structure of NaCl (Rock salt)
• FCC type.
• Co-ordination number 6:6.
• Calculation of no. of atoms of NaCl/unit
cell:
Cl at corners: (8 × 1/8) =1
Cl at face centres (6 × 1/2) =3
Na at edge centres (12 × 1/4) = 3
Na at body centre =1
Unit cell contents are 4(Na+Cl-)
i.e. per each unit cell, 4 NaCl
units will be present.
51. Structure of CsCl
• bcc type.
• Co-ordination number 8:8.
• Number of atoms/unit cell:1
52. Structure of ZnS
• fcc type.
• Co-ordination number
4:4.
• Calculation of no. of
atoms/unit cell:
Total S = 8x1/8 + 6x1/2 = 4
Total Zn = 4
Hence, total ZnS = 4
53. Structure of CaF2
Ca+
F-
• fcc type.
• Co-ordination number: 8:4
(8 for cation, 4 for anion)
*Note: All the compounds of AB2 type follow the same pattern.
54. Structure of K2O
O -2
Na+
• fcc type.
• Co-ordination number: 4:8
4 for cation
8 for anion
57. Structure of diamond
• fcc type.
• Tetrahedral
• C-C bond length = 1.34A
• Refractive index = 2.4
• High dispersive power of light
• Non-conductor of electricity
• 3d network
• Hardest substance ever known.
• Used as abrasive.
60. Structure of Graphite
• One of the softest substances ever known.
• 2-d hexagonal layer structure
• C-C bond length = 1.45A
• Inter layer distance = 3.54A
• Sliding nature
• sp2 hybridisation with one electron left over.
• Specific gravity 2.2
• Electrical conductor
• Metallic lustre
• Used as good lubricant.
63. Important points about Fullurenes
• Discovered in 1985 as C60.
• Consists of spherical, ellipsoid or cylindrical
arrangement of dozens of C-atoms.
• 3 types:
Spherical: Also called ‘bucky balls’. Molecule
of the year 1991 by Science magazine.
Cylindrical: C nanotubes or buckytubes.
Planar.
64. Structure of fullurenes
• 60 C-atoms arranged in pentagons and hexagons.
• 7Å in diameter.
• Soccer-ball shaped molecule with 20 six-membered & 12
five-membered rings.
• Each pentagon is surrounded by five hexagons.
• No two pentagons are adjecent.
• Each carbon is sp2-hybridized.
• Used:
as photoresistant.
in the preparation of super-conductors.
in optical devices.
in batteries as charge carriers.
65. BraGG’S eQuation
X-ray
Tube Detector
Incident radiation “Reflected” radiation 1
2
θ θ
X Z
Y
d
Transmitted radiation
Beam 2 lags beam 1 by XYZ = 2d sin θ
so 2d sin θ = nλ Bragg’s Law