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THE SOLID STATE

TERMS EXPLANATIONS

Amorphous and Crystalline Solids Amorphous- short range order, Irregular shape eg-glass

Crystalline Solids- long range order, regular shape eg : NaCl

Molecular solids Ar, CCl4, H2O (ice)

Covalent or Network solid SiO2 diamond

No of lattice points per unit cell Simple cubic -4, BCC- 9, FCC 14 , End-Centred- 10No of atoms per unit cell (z ) Simple cubic -1, BCC- 2, FCC 4 , End-Centred- 2

Coordination Number FCC- 6:6 BCC- 8:8

Calculation of number of voids Let the number of close packed spheres be N, then:

The number of octahedral voids generated = N

The number of tetrahedral voids generated = 2N

Relation between r and a Simple Cubic a = 2r , BCC 4r = a3 FCC4r = a2

Packing Efficiency Simple Cubic52.4% , BCC 68% , FCC 74%

Calculations Involving Unit Cell

Dimensions

M=molar mass (g/mol) a = edge length in cm ,NA = 6.023 10

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Frenkel Defect: Cation is dislocated to an interstitial site. It does not change the density ofthe solid. Frenkel defect is shown by ionic substance in which there is a

large difference in the size of ions, for example, ZnS, AgCl, AgBr and

AgI due to small size of Zn2+

and Ag+

ions.

Schottky Defect A vacancy defect. The number of missing cations and anions are

equal. Density decreases. For example, NaCl, KCl, CsCl and AgBr.

Metal excess defect due to

anionic vacancies (F-centres )

When NaCl heated in an atmosphere of Na vapour, the Na atoms

deposited on the surface of the crystal. The Cl ions diffuse to the

surface of the crystal and combine with Na atoms to give NaCl. Thereleased electrons diffuse into the crystal and occupy anionic sites

The anionic sites occupied by unpaired electrons are called F-centres

They impart yellow colour to the crystals of NaCl. Similarly, excess

of lithium makes LiCl crystals pink and excess of potassium

makes KCl crystals violet (or lilac).

Doping The conductivity of intrinsic semiconductors is increased by adding

an appropriate amount of suitable impurity. This process is called

doping

n / p -type semiconductors n- type : Si + As or Sb or Bi p-type: Si + B or Ga or In or Tl

13 15 compounds &1216compounds

13 15 compounds: InSb, AlP and GaAs.12 16 compounds :ZnS, CdS, CdSe and HgTe

Paramagnetic substances Weakly attracted by a magnetic field. Examples: O2, Cu2+, Fe3+, Cr3+

Diamagnetic substances Weakly repelled by a magnetic field. Example: H2O, NaCl and C6H6

Ferromagnetism: A few substances like iron, cobalt, nickel, gadolinium and CrO2 are

attracted very strongly by a magnetic field.

Antiferromagnetism MnO. Domains oppositely oriented and cancel out magnetic moment

Ferrimagnetism: domains aligned in parallel and anti-parallel directions in unequal

numbers . Example: Fe3O4 (magnetite)

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