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NEET Chemistry Solid State

Solid State PDF Notes, Important Questions and Synopsis

SYNOPSIS

  • Differences between crystalline solid and amorphous solid:

                          Crystalline Solid

                       Amorphous Solid

    The internal arrangement of particles is well defined.

    The internal arrangement of particles is not well defined.

    There is regularity in the external form when crystals are formed.

    There is no regularity in the external form when amorphous solids are formed.

    These have a sharp melting point.

    These melt over a range of temperatures.

    These have characteristic heat of fusion.

    These do not have characteristic heat of fusion.

    Crystalline solids give a regular cut when cut with a sharp-edged knife.

    Amorphous solids give an irregular cut.

    Crystalline solids are regarded as true solids.

    Amorphous solids are super-cooled liquids or pseudo solids.

    These are generally incompressible.

    These may be compressed to an extent.

  • Classification of crystals into seven systems:

    Crystal system

    Unit cell dimensions and angles

    Bravais Examples

    Lattices

    Cubic

    a = b = c; αβγ= 90°

    SC, BCC, FCC

    NaCl

    Orthorhombic

    c; αβγ= 90°

    SC, BCC, end

    centred & FCC

    S(Rhombic sulphur)

    Tetragonal

    a = b c; αβγ= 90°

    SC, BCC

    Sn, ZnO2

    Monoclinic

    c; αγ= 90°β

    SC, end centred

    S(Monoclinic sulphur)

    Rhombohedral

    a = b = c; αβγ = 90°

    SC

    Quartz

    Triclinic

    c; αβγ90°

    SC

    H3BO3

    Hexagonal

    a = b c; αβ= 90°;γ= 120°

    SC

    Graphite

  • Analysis of cubical system:


     

    Property

    SC

    BCC

    FCC

    •    

    Atomic radius (r)

    a = edge length

     begin mathsize 12px style straight a over 2 end style  begin mathsize 12px style fraction numerator square root of 3 straight a over denominator 4 end fraction end style  begin mathsize 12px style fraction numerator straight a over denominator 2 square root of 2 end fraction end style
    •         

    No. of atoms per

    unit cell (Z)

     

    1

     

    2

     

    4

    •       

    C. No.

    6

    8

    12

    •               

    Packing efficiency

    52%

    68%

    74%

    •                     

    No. of voids

    (a) octahedral (Z)

    (b) tetrahedral (2Z)

     

    -

    -

     

    -

    -

     

    4

    8



  • Neighbourhood of a particle:
  1. Simple cubic (SC) structure:

    Type of neighbour

    Distance

    No. of neighbours

    nearest

    a

    6 (shared by 4 cubes)

    (next)1

    begin mathsize 12px style straight a square root of 2 end style

    12 (shared by 2 cubes)

    (next)2

    begin mathsize 12px style straight a square root of 3 end style

    8 (unshared)

  2. Body-centred cubic (BCC) structure:

    Type of neighbour

    Distance

    No. of neighbours

    nearest

    begin mathsize 12px style 2 straight r equals straight a fraction numerator square root of 3 over denominator 2 end fraction end style

    8

    (next)1

    =a

    6

    (next)2

    begin mathsize 12px style equals straight a square root of 2 end style

    12

    (next)3

    begin mathsize 12px style equals straight a fraction numerator square root of 3 over denominator 2 end fraction end style

    24

    (next)4

    begin mathsize 12px style equals straight a square root of 3 end style

    8

  3. Face-centred cubic (FCC) structure:

    Type of neighbour

     

    Distance

    No. of neighbours

    nearest

    begin mathsize 12px style fraction numerator straight a over denominator square root of 2 end fraction end style begin mathsize 12px style 12 equals open parentheses fraction numerator 3 cross times 8 over denominator 2 end fraction close parentheses end style

    (next)1

       a

    begin mathsize 12px style 6 equals open parentheses fraction numerator 3 cross times 8 over denominator 4 end fraction close parentheses end stylebegin mathsize 12px style 6 equals open parentheses fraction numerator 3 cross times 8 over denominator 4 end fraction close parentheses end style

    (next)2

    begin mathsize 12px style straight a square root of fraction numerator 3 over denominator square root of 2 end fraction end root end style

    24

    (next)3

     begin mathsize 12px style straight a square root of 2 end style

    12

    (next)4

    begin mathsize 12px style straight a square root of fraction numerator 5 over denominator square root of 2 end fraction end root end style

    24

Packing of constituents in crystals:

  Structure

 Packing                           pattern

 Coordination number

Packing efficiency (%)

Unit cell

Simple cubic

AAAA

        6

      52

 Primitive cubic

Body-centred cubic or BCC

ABAB

        8

      68

Body-centred cubic

Hexagonal closed packing

ABAB

        12

      74

Non-cubic

Cubic closest packing or FCC

ABCABC

        12

      74

Face-centred cubic

  • Ionic crystals:

    C. No.

    Limiting radius ratio begin mathsize 12px style open parentheses straight r subscript plus over straight r subscript minus close parentheses end style

    3

    0.155 - 0.225 (triangular)

    4

    0.225 - 0.414 (tetrahedral)

    6

    0.414 - 0.732 (octahedral)

    8

    0.732 - 0.999 (cubic)

  • Crystal defects (Imperfections):

    • Stoichiometric effect:
    • Schottky defect:

Frenkel defect:
•This defect is created when an ion leaves its correct lattice site and occupies an interstitial site. Examples: ZnS, AgCl, AgBr, AgI

Non-stoichiometric effect:

Metal excess defect:

  • These defects arise due to anionic vacancies.
  • This type of defect is exhibited by alkali halides. Examples: NaCl, KCl

Metal deficiency defect:

  • These defects arise when a compound has metal deficiency due to the absence of a metal ion from its lattice site.
  • This type of defect is generally found in compounds of transition metals. Examples: ZnO, CdS