Solid State in One Page

THE SOLID STATE TERMS Amorphous and Crystalline Solids Molecular solids Covalent or Network solid No of lattice points per unit cell No of atoms per unit cell (z ) Coordination Number Calculation of number of voids

Relation between r and a Packing Efficiency Calculations Involving Unit Cell Dimensions

EXPLANATIONS Amorphous- short range order, Irregular shape eg-glass Crystalline Solids- long range order, regular shape eg : NaCl Ar, CCl4, H2O (ice) SiO2 diamond Simple cubic -4, BCC- 9, FCC – 14 , End-Centred- 10 Simple cubic -1, BCC- 2, FCC – 4 , End-Centred- 2 FCC- 6:6 BCC- 8:8 Let the number of close packed spheres be N, then: The number of octahedral voids generated = N The number of tetrahedral voids generated = 2N Simple Cubic a = 2r , BCC 4r = a√3 FCC 4r = a√2 Simple Cubic52.4% , BCC 68% , FCC 74%

NA = 6.023× 1023

M=molar mass (g/mol)

a = edge length in cm ,

Frenkel Defect:

Cation is dislocated to an interstitial site. It does not change the density of the 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. 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. The released 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). The conductivity of intrinsic semiconductors is increased by adding an appropriate amount of suitable impurity. This process is called doping n- type : Si + As or Sb or Bi p-type: Si + B or Ga or In or Tl 13 – 15 compounds: InSb, AlP and GaAs. 12 – 16 compounds :ZnS, CdS, CdSe and HgTe Weakly attracted by a magnetic field. Examples: O2, Cu2+, Fe3+, Cr3+ Weakly repelled by a magnetic field. Example: H2O, NaCl and C6H6 A few substances like iron, cobalt, nickel, gadolinium and CrO2 are attracted very strongly by a magnetic field. MnO. Domains oppositely oriented and cancel out magnetic moment domains aligned in parallel and anti-parallel directions in unequal numbers . Example: Fe3O4 (magnetite)

Metal excess defect due to anionic vacancies (F-centres )

Doping

n / p -type semiconductors 13 –15 compounds &12–16 compounds Paramagnetic substances Diamagnetic substances Ferromagnetism: Antiferromagnetism Ferrimagnetism: