Stoichiometric Defects. Defects in Stoichiometric Solids. It is generally known that all the compounds follow law of definite proportion. But there are certain solid compounds which, refuse to obey this universal law. In non-stoichiometric or Berthollide compounds the ratio of the number of atoms of one kind to the number of atoms of the other kind does not correspond exactly. Fundamentally, although ionic radii may offer some guidance as to defect formation, the bottom line is that the silver halides have complex bonding energetics.
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In vacancy defects, an atom is missing from its regular atomic site. Stoichiometric defects of missing of atom the density of substance decreases, i.
stoichiometric defects The vacancy defect develops on heating of substance. In interstitial defect, some atoms occupy sites at which; generally there is no atom in the crystal structure.
Because of the interstitial defects, the number of atoms becomes larger than the number of lattice sites. Increase in number of atoms increases the density of substance, i.
The vacancy defects and interstitial defects are found only in non-ionic compounds. stoichiometric defects
Class 12 CBSE Chemistry - Solid State - Imperfections in Solids
Such defects found in ionic compounds are known as Frenkel Defects and Schottky Defects. It is a type of vacancy defect. In ionic compounds, some of stoichiometric defects ions usually smaller in size get dislocated from their original site and create defect. Metal excess defect due to the presence of extra cations at interstitial sites: In this case, there are extra positive ions occupying interstitial sites stoichiometric defects the electrons in another interstitial sites to maintain electrical neutrality.
The defect may be visualised as the loss of stoichiometric defects atoms which leave their electrons behind. The excess metal ions occupy interstitial positions.
The common example is Zinc Oxide. Since cations are usually smaller than anions, they occupy interstitial sites.
Non-Stoichiometric Defects | AMAZING SOLIDS
This type of stoichiometric defects occurs in the compounds which have low co-ordination number and cations and anions of different sizes. But stoichiometric defects are certain solid compounds which, refuse to obey this universal law. Such solid compounds which actually do not possess the exact compositions according to the electronic considerations have been given the name Berthollide or non-stoichiometric compounds.
For example, in certain oxides such as Metallic hydrides as; tungsten bronzes asetc.
Physical chemistry - Stoichiometric defects in silver bromide - Chemistry Stack Exchange
It is clear stoichiometric defects such an unbalance of composition is only possible if the structure is in some way irregular that it possesses defects. Non-stoichiometry means there is an excess either of metal or of non-metal atoms.
It is also called dislocation defect. It does not alter the density of stoichiometric defects solid.
This defect in ionic solids is equivalent to the vacancy defect in non-ionic solids.