L11 : 7 seven Lattice system - Solid States , Chemistry, Class 12 Video Lecture

hello friends this video and solid
states part 11 is brought to you by exam
Viacom no more fear from exam so as we
have told that crystal lattice are made
of unit cells and the crystal the unit
cell has parameters alpha beta gamma
MinC if you value this parameters a B
and C n alpha beta gamma you get
different varieties of unit cells
correct experimentally it has been seen
that there are only four different types
of unit cells based on alpha beta gamma
and ABC and they are called seven
lattice system and their name is
monoclinic triclinic orthorhombic
rhombohedral make tetrahedral hexagonal
and cubic so if you see this was a
generic definition of unit cell this is
what we have discussed we have K B and C
alpha beta gamma so you there is
parameter example in Q everything is
same a B and C are same
Alpha Beta Gamma is same so in cubic
form E is equal to B it is equal to C
and alpha is equal to beta is going to
come all are equal and this is 1 9
degree actually 9 degree and you get
something called cubic in tight diagonal
if a is equal to P but not equal to C
two sides are equal this is a let's
suppose and this is a but this is B two
sides are equal third side is not equal
right in that case but the angles are
equal and they are 90 this is called
Kate lacunae in orthorhombic all the
sides are unequal they are earning
unequal sides that is is not equal to B
is not equal to C but alpha is equal to
beta is going to come
is equal to 90 that is called
orthorhombic they also want something
called monoclinic where sides are not
equal
sorry is not equal to B is not equal to
Z sides are not equal when I talk about
the angle alpha two angles are equal and
they are ninety three you see alpha and
beta in the two angles are equal on
yourself and B time theory and gamma is
not equal to 120
it is monoclinic two angles are my
integral third angle is not 120 correct
then we have something called hexagonal
in hexagonal everything is defined what
is defined two sides are equal you have
a here the signs also a right that means
two sides are equal that is is equal to
B but third side is not equal but
angular also define two angles are 90
and one angle 120 V Z so you can see
that alpha is equal to alpha is equal to
beta is equal to 90 degree and gamma is
equal to 120 right is he all the angles
also defined in case of rhombohedral
what we do is all the sides are equal he
is going to be it's good to see all the
angles are also equal but they are not
equal to 90 this is like a cube you take
a cube and you just tilt the cube root
right you apply some force in this
direction maybe it will be tilted you
get wrong word then you have something
called cycling and dry cleaning all the
sides are unequal busy all the sides of
million ABC all the angles are different
that's why you see all the angles are
majorly
hey alpha is not equal to beta is not
equal to gamma and they are not going to
get equal to nine leave these seven
systems are something which is form
experiment that is a structure of these
unit cells but the way the atoms are
arranged in this unit cells maybe as in
some case the atoms are in union the
corners in some case of miss atoms
arranged also in the center in some
cases atoms are arranged in the face you
don't know right so that is a different
story all together so that is a category
so and elphic only one unit cell norm
and we will see that this unit cells
also have various categories the first
is the primitive cells in this case all
the constituent particles which have is
ions molecules atoms they are present
only on the corners only on corner
correct then we have center unit cells
and central unit cells the constant
particles are present in the corner also
somewhere else right somewhere else
maybe say the body inside this edges we
don't know some a in the corner corner
plus somewhere else somewhere is all
somewhere else to correct in this there
are three types the one is the body
centered in body centered the atoms or
the constant particles represent in the
corners plus center of the body that's
why the name body centered center of the
body correct that is my body centered
the next is face centered face centered
coordinates plus all the face I shown
half one because half is will be the
part of another unit cell because
there'll be so many units will combine
right so just for the clear view this is
half shown here will be full actually
when the part of this is only half so
just for a better view action on the
half
items here so they are shown they are on
the all
four or one two three four five six six
sides correct plus corner so center of
each of the face so each six phase plus
common let's say center of each field
because they are in center of each six
phase then we have the last one called M
Center so n centered center of any other
two opposite face may be on these two
face or these two face right like that
or this to face the three possible
options and that's why the name is a B
or C it is the a a phase or B phase or
CVS so primitive is called by letter P
the body centered by later I face
centered by F and n centered either by a
B or C depending on its on the edge a or
HBO AC right there are four different
categories of unit cells thank you
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