THE SOLID STATE Class XII Chemistry by TEACHING CARE online tuition and coaching classes

THE SOLID STATE Class XII Chemistry by TEACHING CARE online tuition and coaching classes


Types of solid on the basis of the arrangement of component particles :

Crystalline Solid Amorphous Solid
(i) The constituent particles are arranged in a definite geometrical pattern (i) The constituent particles are not arranged in any regular fasion.
(ii) They are anisotrophic in nature (ii) They are isotrophic in nature
(iii) Melt at a sharp characteristic temperature (iii) Gradually soften over a range of a temperature
(iv) True solid (iv) Pseudo solid or super cooled liquid
(v) They have a definite and characteristic heat of fusion (v) They do not have definite heat of fusion


  • The value of same physical property is found to be same along any direction. Anisotropic : The value of same physical property is found to be different along each direction unit cell. The smallest three dimensional portion of a complete space lattice which when repeated over and again in different direction produces the complete space lattice is called unit cell.
  • Space Lattice : such a regular arrangement of the constituent particle of a crystal in a 3-d space is called space lattice.
Properties Molecular Ionic Metallic Covalent
(i) Component particles Molecules Ions Metallic care Atoms
(ii) Nature of binding force Vandar Wall Ionic Metlalic Covalent
(iii) Melting point Very low High Quite high High
(iv) Electrical conductance Insulator Insulator(s) conductance Good Conductor Insulated exept
(v) e.g. Ice NaCl Al, Cu Dia
  • 7 Crystal System : Cubic, tetragal, arthorhombic, monoclinic, hexagonal, rhombahedral, triclinic.

Types of unit cell :

(i) Primitive Unit no. of particle

(ii) Face centred unit cell (FEC) no. of particle

(iii) Body cenred unit cell (BCC) no. of particle

(iv) Edge centred unit cell (ECC) no. of particle

Close Packing of Sphere :

(i) Packing over hexagonal 2-d.

(a) ABAB (packing)

(b) ABC.ABC (cubic close packing)

(ii) Packing over square close packing AAA.AAA packing.

Co-ordination number : The number of closest neighbours of any constituent particle is termed as


  • The unoccupied space in between the sphere are called voids.
  • Tetrahedral void = 0.225
  • Octahedral void = 0.414
  • Triagonal void = 0.155

No. of octahedral voids = n

No. of tetrahedral voids = 2n

No. of trigonal voids = 8n

  • Packing efficiency : Packing efficiency in hcp/ccp/fcc : –

Total volume

Volume of a unit cell

Packing efficiency

Similarly :

Packing efficiency in BCC = 68%

Packing efficiency in SCC = 52.4%

Ionic compound C.N. Z
(i) NaCl 6 : 6 4
(ii) CsCl 8 : 8 1
(iii) CaF2 8 : 4 4
(iv) Na2O 4 : 8 4



Where d = density.

Z = No. of particles.

M = molecular mass

NA = 6.022 × 1023

a = edge of unit cell.

  • Contribution made by each particle to each unit cell :

(i) Corner =

(ii) Face centred =

(iii) Body centred = 1

(iv) Edge centred =

Point defect : Point defect are the irregularities from ideal arrangement around a point on an atom in a crystallation substance.

Schottky Defect Frenkel Defect
(i) It decreases the  density of substance (i) Density remain constant
(ii) Cation and anion leave their original site (ii) Cation same occupied void sphere
(iii) More ionic character (iii) Less ionic character
(iv) More co-ordination number (iv) Less co-ordination character


Non Stoichometric Point defect :

  • Metal excess defect due to any vacancies.
  • Metal deficiency defect due to loss of cation.
  • Metal excess defect due to the presence of extra cations at interstitial sites.

Types of Solids on the basis of their electrical conductivity :

  • Conductor : Solid with conductivities ranging between 104 to 107 ohM–1M–1. e.g. Metals.
  • Insulator : Solids with conductivities ranging between 104 to 107 ohM–1M–1.
  • Semiconductor : solids with conductivities ranging between 10–6 to 10–10

Conduction of Electricity in Metals

  • A conductor may conduct electricity through movement of electrons or ions.
  • Metals conduct electricity in solid as well as Molten State.

Conduction of Electricity in Semiconductors

  • In case of semiconductors, the gap between the valence band and conduction band is small. Therefore, some electrons may jump to conduction band and show some conductivities.
  • Electrical conductivity of semi-conductors increases with rise in temperature.

Intrinsic Semi-conductors – Silicon and germanium.

  • Doping : The process of increasing conductivity of intrinsic semi-conductor by mixing appropriate amount of suitable impurity.

Types of Impurities :

  • (i) Electron rich impurities.
  • (ii) Electron deficit impurities.
  • Electron rich impurities forms n-type semiconductor.
  • Electron-deficit impurities forms r-type semiconductor.
  • Application of n-type and r-type is used for making electronic components.
  • Diode is a combination of n-type and r-type semiconductors and is used as a rectifier.
  • npn and pnp are used to detect or amplify radii or audio signals.
  • Used in solar cell for conversion of light energy into electrical energy.
  • Magnetic Properties : On the basis of their magnetic properties, substances can be classified into five categories.
  • Paramagnetism : Paramagnetic substances are weakly attracted by a magnetic field. They are magnetized in a magnetic field in the same direction. They lose their magnetism in the absence of magnetic field. It is due to presence of one or more unpaired electrons which are attracted by the magnetic field. e.g. O2, Cu2+, Fe3+, Cr3+.
  • Diamagnetism : Diamagnetic substances are weakly repelled by a magnetic field. they are weakly magnetized in a magnetic field in opposite direction. Shown by which are paired. e.g. H2O, NaCl, C2H6.
  • Ferromagnetism : A few substances like iron, cobalt, nickel are attracted very strongly by a magnetic field. such substance are called ferromagnetic substances.
  • Antiferromagnetism : Substances like MnO showing antiferromagnetism have domain structure similar to ferromagnetism substance, but their domains are oppositely oriented and cancel out each other’s magnetic moment.
  • Ferrimagnetism : Ferrimagnetism observed when the magnetic moments of the domains in the substance are aligned in parallel and anti-parallel directions in unequal number. They are weakly attracted by magnetic field as compare to ferromagnetic substance. e.g. Fe3O4 and MgFe2O4.


Solved questions








  1. What is the coordination number of hcp and ccp?
  2. How many atoms are there in a unit cell of a metal crystallizing in fcc structure.
  3. The unit cell of a substance has a cations A+ at the corners of the unit cell and the anion B in the centre. What is the simplest formula of the substance?
  4. What is the co-ordination number of each sphere in cubic close packing of spheres in three dimensions?
  5. What is the effect of temperature on the conductivity of a semiconductor?
  6. What is the effect of the presence of Schottky defect on the density of a crystal?
  7. What is Frenkel defect?
  8. How is ferromagnetism different from paramagnetism?
  9. A metallic element crystallizes into a lattice containing a sequence of layers AB AB AB …. Any packing of spheres leaves voids in the lattice. What percentage by the volume of this lattice is empty?
  10. Why does KCl turn violet on heating in potassium vapour?


  1. A solid A+ B has NaCl type close packed structure. If the anion has a radius of 250 pm, what should be the ideal radius of cation? Can a cation C+ having a radius of 180 pm is slipped into the tetrahedral site of the crystal A+ B? Give reason for your answer.
  2. Predict the closed packed structure of an ionic compound A+B in which the radius of cation is 148 pm and radius of anion is 195 pm. What is the coordination number of cation?
  3. Predict the structure of MgO crystal and coordination number of its cation in which cation and anion radii are equal to 65 pm and 140 pm respectively.
  4. Chromium crystallizes in a body-centred cubic lattice whose density is 7.2g cm–3 The length of the edge of a unit cell is 288.4 pm. Calculate Avogadro’s number.
  5. The compound CuCl has ZnS structure and the edge of the unit cell is 500 pm. Find its density.

          [Agogadro’s number = 6.023 × 1023. At. Mass of Cu = 63 and Cl = 35.5]

  1. The density of KBr is 2.75 g cm–3. The length of edge of the unit cell is 654 pm. Show that KBr has a face-centred cubic structure.
  2. An element (density 6.8 g cm–3) occurs in bcc structure with cell edge of 290 pm. Calculate the number of atoms present in 200 g of the element.
  3. Crystalline CsBr has bcc structure. Calculate unit cell edge length if density of CsB crystal is 4.24 g cm–3.
  4. An Element ‘A’ crystallizes in fcc structure. The 208 g of it has 4.2832 × 1024 atoms. Calculate the edge of the unit cell if the density of ‘A’ is 7.2 g cm–3.


  1. What are point defects? Describe Schottky and Frenkel defects. What is the difference between the two?
  2. (a) How many atoms are there in a body-centred cubic cell?

          (b) Calculate the number of atoms in a cubic unit cell and having one atom on each corner and two atoms on each diagonal.

(c) A solid substance AB has a rock salt geometry. What is the coordination of ‘A’ and ‘B’? How many atoms of ‘A’ and ‘B’ are present in the unit cell?

  1. Calcium oxide crystallizes as one of the three cubic crystalline structure. The length of the edge of the unit cell is 481 pm and density of calcium oxide is 3.25 g cm–3. How many formula units of CaO are there in a unit cell? Does the unit cell have NaCl or CsCl structure.
  2. Tungsten has a density of 19.35 g cm–3 and length of the side of the unit cell is 316 pm. The unit cell has a body-centred unit cell. How many atoms of the element does 50 g of the element contain?
  3. Calculate the density of silver which crystallizes in the face-centred cubic structure. The distance between the nearest silver atoms in the structure is 287 pm. [Molar mass of Ag = 107.87; NA = 6.023 × 1023].
  4. Iron(II) oxide has a cubic structure and each unit cell has the side 5 Å. If the density of the oxide is 4 g cm–3, calculate the number of Fe2+ and O2– ions present in each unit cell. [Molar mass of FeO = 72 g/mol; NA = 6.023 × 1023].