Stoichiometric Defects Video Lecture - JEE

hello friends this piggy on solid states
part 20 is brought to you by exam Pierre
calm no more fear from exam talk about
imperfections in science nothing is
perfect in this world everybody has some
imperfections so in the crystals so this
is the sodium chloride crystals and if
you see there are some impurities all
right
so crystals are also not perfect so one
solid has large number of twists so
defect in crystal happens during
crystallization process so if the
crystallization process is very fast it
will become amorphous it see the own
beaning crystals if it is slow but not
that stores moderate store it will be
some defect it's very very slow then you
may get him then you may get a perfect
crystal but that's very rare very rare
generally you have some defect so I
throw this imperfection in the fish in
this solids is because of the
crystallization speed actually and we
have discussed that right so for very
good quality of crystallization of a
very good quality of crystals the
crystallization should offer at a very
very slow speed but even if you do it at
very very slow set some defect
are bound to occur and other this
defects this defects nothing but their
regularity in arrangement if you see
there was an arrangement something else
came some gap came these are my
irregularity in the arrangement they are
two types out of it one is the point
defect where you have defect at one
point example the one lattice come on or
two lattice point example in this case
sodium chloride is a defect here is a
defect here so they have defects or
irregularities or deviation from the
ideal arrangement and on the point right
then they are something online defect in
line defect we have the whole
irregularity or deviation in the entire
row of lattice for example this is all
division here is you mean it has to be
all green they some red here here
assuming it has to be all green and
purple there are some red here this Reds
are a deviation this is point defect
defects point at only some lattice
points line defect defects in the entire
row so we will focus only on the point
defects in this chapter right so point
defects are also of two types
stoichiometric defects in stoichiometric
defects we have vacancy defects
interstitial defect fine clean defects
costly defects we have infinite defect
and nonzero entry divots
you have these many types of defects
since documented effects actually the
stock Yuma Tori of the substance solid
is not impacted in non stoichiometry
defect the Soyka matter is impacted and
impurity we have extra impurity the
foreign elements are there in this one
elements are there so we'll discuss
these type of events
we'll start with and in sorry in a
non-story entity but we have met Alexis
defect in metal deficient defect
so we'll start with this effect on the
force is stoichiometric liver it is a
point defect type right and this defect
does not disturb the stoichiometry of
the soil note these defect does not
impact
stoichiometry of sorry let me know for
an element in this so we see here this
is a gap created right this is a defect
there is a gap here this is a defect
hollow correct so this is the stock
mentalism so here two types of shock
material let's discuss that the first is
the vacancy defect so in vacancy defect
what happens is some lattice sites are
vacant if you see here let's assume
these are valid resides
these are vacant here correct since some
of the sites are vacant the density is
less this vacancy defect this will
decrease density here some lattice sites
are Arabic it that it is jelly shown by
non ionic because for ionic there is a
complex tool if glass is missing there
has to be one - also missing so that
it's neutral right the charge
distributed is not a different story
altogether we'll discuss that this is
only for non ionic so the next is
interstitial defect so in this what
happens is in this extra interstitial
position right some atoms comments stay
there so the definition is when the
Constituent particles some of the
constant particles occupy the
interstitial site these are called
interstitial site I like the space in
the voids in the question is called
interstitial site so when the sum of
constituent particles occupy the
interstitial site it is called
interstitial defect in fact it will
increase the density right see
these are extra these are extra in the
same pack in the same unit cell they're
extra it landmass the system since it
add Marshman system density is mass per
volume volume is constant mass is
increasing that means the density has to
increase it is also by non ionic only
correct so what happens in the case of
ionic so let's see in case of onyx
I need must maintain neutrality because
the compound is not returned it not be
stable it must maintain neutrality so
the other than simple vacancy or
interstitial defect here we have Frankel
and Scot clicker example is NaCl if you
see na plus co - have this ionic form so
let's see the Frankie living so this is
a regular arrangement of NaCl let's
suppose right I have my na plus here and
Cl minus here now what happens is
smaller ions are this local tin from the
normal size - interstitial site click so
you see here in our case na plus is
smaller so na went from here to here
correct one more na went from here to
here
let's see once again one na went from
it's normal protein to another place and
one na also went from normal situ
interstitial site right I also call
dislocation defect because there is
nothing except but some dislocation
happening this location
defect nothing is missing right the
whole system is intact the number of
atoms that should be in a crystal is
same only thing is they are dislocated
so density is not changed there is no
change in density I'm sorry and examples
are Gelinas agcl AG BR bromide single
provides the iodide all these show this
kind of better correct and this is
generally shown the criteria worst since
the one smaller ions move so there has
to be difference in the size right one
has to be a smaller so difference in
size is required here difference in ion
size favors this kind of defect the
smaller ones dislocated the next is
Scott cave now scoffs key defect
something is missing but in order to
maintain the neutrality what would
happen is the number of cation missing
should be equal to the number of and I
am missing so if you miss remove only
one negative charge then the whole
crystal becomes positively charged we
don't want that so one positive charge
also should go off right something like
this you see right one person even
negative went on this kind of defect is
called skorsky dipping and since to cata
one cation anion in this case which I
showed you or n number of cations anions
pairs are removed from this so density
will obviously decrease correct why
because density is mass where volume
mass is decreasing volume is constant
for a crystal correct here LS here is a
good example and NaCl we have almost one
costly defect one defect in 10 to the
power 6
the experimental value so it is
generally shown by substance which has
similar cations and anions sighs goodbye
on an online place the last effect was
not shown - in this divot - so - here
correct other examples as potassium
chloride yes he l AG BR etcetera
please note a g BR shows both difficult
age e BR is special the special kind it
shows both the defect Scott kid if again
thank you thank you
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