Video: Crystal Lattice and Unit cells Video Lecture - Class 12

hello friends this video on solid state
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next we'll discuss the crystal lattice
now we have discussed about the various
types of crystal solids right now let's
understand let's go deep into the
crystal and understand the crystal
lattice how the crystals are formed so
we have seen that the main feature the
main feature of crystalline solid is the
regular and the repeating pattern of
Constituent particles correct that's
what we have heard so many times the
cost crystalline solid that means
regular and repeating pattern of
Constituent particles see we see the
regular in the regular 3d arrangement of
point and space is called crystal
lattice let me write this
what is crystal lattice it is nothing
but a regular 3d arrangement of points
in space
so you see this is a 3d arrangement of
NSEL right this is also 3d arrangement
of silicon this is also 3d arrangement
of carbon graphite so if you see these
are all 3d arrangement this is feederism
of an A plus Co - so these 3d
arrangement is called crystal lattice we
will see will tell that this is the
crystal lattice of sodium chloride this
is the crystal lattice carbons which
logic of silicon so crystal lattice is
also called periodic and systematic
arrangement of atoms for non crystal
current please note it is not found in
amorphous solid or gas you don't have
pistol and because crystal address it
has to be irregularly and see the
regular word is there so regular word
doesn't comes in amorphous correct so
just like this regular 3d arrangement
not points in space so why we are
studying crystal addressable cushion the
physical properties we have discussed
now the malleability ductility or
various other physical property the
electrical conductivity so those things
actually depends on this crystal lattice
then ami just come on melting point
boiling point on a very high view but
actually you want to understand deep for
a given compound why this compound
behaves in Xyz manners you have to
understand the crystal lattice it is
very very critical because this crystal
lattice explains the physical properties
of a crystal correct so since crystal
lattice is very critical to us kiss
understands all the properties of
characteristic of the critter lancret
lattice points see this crystal lattice
each point in this crystal lattice is
called at this point you see these all
other smile
a letter size each point in this crystal
lattice it represents one of the caustic
constituent particles it may be atom
molecules I example in this case this is
mine na plus ions it is my single main
facts so each of these points will
represent a constituent particle correct
so each point is called at this point or
lattice site you know each all this
lattice sites is nothing but a
constituent particle and these lattice
points are joined together for example
this and this point they'll be joined
together by a line and why it is done
just to give a geometry to this lattice
just to you it doesn't make much sense
they all watch your lines do not exist
actually you see your particular
compound in using the x-ray diffraction
techniques you won't see me lies I just
joined the about a geometry to this
lattice to just understand it better
right now let's talk about unit cells
this lattice itself you see a big
lattice right if you can do understand
you'll be able to understand the concept
this lattice is further divided into
unit cells unit cells are the building
block actually so what are unit cells so
units is the smallest portion of crystal
lattice which when repeated generates
entire let's remember this you get from
this so if you see if example if I'm
want to draw
you
so if you if you take this ocean out you
will get this these are my sodium that
is my chlorine correct so chlorine
occupy this corner place and these are
the spaces voids sodium occupies this so
this is my unit cell right the smallest
portion because this itself you keep
repeating it you'll get the lattice so
that is the bigger picture right but the
unit cell is the building block of the
legs because you keep repeating this
unit cell you will get the entire
lattice to understand the lattice is the
bigger picture
whenever I talk about this is my lattice
it has so many unit cells unit cell is
the basic building block smallest
portion of the crystal all right if you
want to see in this figure you can see
in this three-dimensional view one more
view where we have these are my curium
since the sodium is in the voids the
empty space I am not shown sodium here
but sodium will be somewhere here in
here like that all right
what the pictures are same actually will
take you to a video we really understand
all these shapes in the Metroid now let
us understand some characteristic of
unit cells so its dimensions have has
three dimensions address three ages ABC
and these ages may or may not be
appended and the angle between the edges
is alpha beta and gamma so if you see
this is my unit cell it will have
normally cube or cubed or hexagonal
shapes the three dimension same it has
three edges a B and
these is just made me maybe evil may not
be equal maybe perpendicular may not in
a particular right and the angle is
alpha beta comma so if you see alpha is
the angle between B and C alpha is the
angle between alpha angle B and C beta
is the angle in H gamma is the angle
written be it correct so alpha you move
the a bit pc beta remove BB dancing the
remaining eminence now and these angles
so to define the unit cell you need six
parameters hope I understand because if
you make a B and C equal an alpha beta
gamma 90 degree you will get one you get
a shoe boy correct you get a cube Ashley
where ABC are equal and alpha beta comma
90 and you say is not equal to B is not
equal to C but alpha beta gamma are
equal and they are 90 degree then you
get cuboid something like this all right
so based on by changing this parameter
side a B and C and alpha beta gamma you
get different types of Units correct so
unit cells are the basic building of
lattice unit cells is nothing but a
3-dimensional box kind of thing correct
it is either cube Q by their various
unit cells and the parameter is for unit
cells is alpha beta comma a B and C ABC
are the lengths of this unit cell Alpha
Beta Gamma angles so they are various
possible unit cells we'll discuss that
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