Defects in Solids - The Solid State, Chemistry, Class 12 Video Lecture

defects in solids in this module you
will learn about the various types of
point defects present in the crystal
lattice of solids crystalline solids
have a regular arrangement of the
Constituent particles
however this regular arrangement is
sometimes interrupted by certain defects
in the crystal such as point defects and
line defects a defect arising due to the
irregularity in the arrangement of the
Constituent particles around the single
lattice point is referred to as the
point defect on the other hand a digital
delay gravity in the arrangement of the
Constituent particles across the row of
lattice points is referred to as the
line defect in this module we are going
to explore the point defects which are
of three types the stoichiometric non
stoichiometric and impurity defects the
stoichiometric defects are so called
because they do not bring any change to
the structure mentally of the solid
these defects exist in the crystals of
non-ionic as the Lance ionic solids in
the case of non ionic solids the
stoichiometric defects exist in two
different forms vacancy defects and
interstitial defects a vacancy diffict
arises when a constituent particle
leaves its lattice sites creating a
vacant site in the crystal lattice
alternatively an interstitial defect
arises when a constituent particles
occupies an interstitial site in the
lattice on the other hand in case of
ionic solids the stoichiometric defects
exist as Frenkel defect and Schottky
defect in both the Frankel and Schottky
defects the electrical neutrality of the
substance remains maintained Frenkel
defects arrive in the ionic crystals
having large difference in the size of
the constituent iron
in such defects the smaller iron
dislocates from ecstatic site to an
interstitial site Scott a defect on the
other hand arrived in ionic crystals
having contigent ions of similar size in
such defects equal number of cations and
anions leave their lattice site and
create vacancy in the crystal so far you
have learnt about the defect that
maintained the stoichiometry of a
crystalline substance however there are
certain defects that change the
stoichiometric of a crystal these
defects are called non stoichiometric
defects non stoichiometric defects are
of two times metal Excel and metal
deficiency defects the metal excess
defects arise due to two reasons in the
presence of an ionic vacancies in the
crystal of the presence of extra metal
ions let's first understand the metal
excess defects that arrive due to an
ionic vacancies in the crystal when
sodium chloride is heated in the
atmosphere of sodium vapors and then
some sodium atoms get deposited over the
surface of the crystal some of the
chloride ions diffuse from the lattice
sites to the surface and combined with
the sodium atoms to form sodium chloride
the electrons lost by the sodium atoms
in the field inside the crystal and
occupy the sites located by the chloride
ions these sites are called the F
centers such a crystal of sodium
chloride therefore has an excess of
sodium metal and thereby develop the
metal excess defect let's now consider
an example to explore the metal excess
defect that's arise due to the presence
of extra metal ions when zinc of five is
heated some oxygen gas is released from
it during any extra metal ions and
freely across the Duce during the
reaction occupy the interstitial solids
thereby developing the metal excess
these
in the crystal now that you have learned
about the non-stoichiometric metal it
says defects let's learn about the
second type of non stoichiometric
defects the metal deficiency defects the
metal deficiency defects arise when a
crystal becomes deficient of the metal
on losing some metal ions from their
sides in such a case to maintain the
electrical neutrality some of the
remaining cations acquire extra positive
charge by moving into the higher
oxidation state for example in the
crystal of ferrous oxide a few ferrous
ions move out from the site resulting
into a non stoichiometric defect some of
the remaining ferrous ions acquire
higher oxidation state and become ferric
ions let us now learn about the last
type of point defects found in crystal
lattices of solids the impurity defects
an impurity defects arises when a cation
leads its site and some fallen cation
occupies the vacated time such defects
are found to occur in crystal lattice of
sodium chloride when some lattice sites
vacated by sodium ions are occupied by
the in strontium iron to maintain the
electrical neutrality of the crystal one
strontium iron replaces two sodium ions
so half of the vacated times are
occupied by the in function ions while
the other half remained vacant let's
summarize what you have learned in this
module on the basis of their locations
the defects in the crystal axis are
divided into two tiles point defects and
line defects
point defects are the irregularity in
the arrangement of constituent particles
located around one lattice point while
line defects are the irregularity in the
arrangement of constituents in an entire
row of lattice points point defects are
of three times
it stoichiometric non stoichiometric
impurity in stoichiometric defects no
change occurs in this core chemically of
the constituents these defects are
further divided into two targets vacancy
and interstitial vacancy defects arise
when a constituent particle leaves its
lattice site while interstitial defects
arise when a constituent particle
occupies some interstitial site non
stoichiometric defects lead to the
change in the structure metric of the
Constituent particles it is of two types
metal excess defects and metal
deficiency defects metal excess defects
arise either due to the anion vacancy in
the crystal or due to the presence of
extra metal ions in the crystal on the
other hand metal deficiency defects
arises when a crystal becomes deficient
of the metal an impurity defect cations
in the crystal lattice lead their sides
and some foreign cations occupy the
vacated site to maintain the electrical
neutrality