Solids, Its Properties, and the Intermolecular Forces | Crystalline Solids and Amorphous Solids
Summary
TLDRThis video script explores the properties of solids, distinguishing between crystalline and amorphous solids. Crystalline solids have a regular, repeating structure, like diamond and ice, while amorphous solids lack long-range order, such as glass and rubber. The script delves into the concept of crystal lattices and unit cells, explaining how they dictate a material's properties. It also touches on the significance of atomic packing and the use of X-ray diffraction to determine crystal structures, providing a comprehensive foundation for understanding solid-state chemistry.
Takeaways
- 🧊 Solids have a rigid structure distinguishing them from liquids and gases, where atoms, ions, or molecules are usually locked into place.
- 🔍 The arrangement of particles in a solid can be either crystalline, with a regular repeating pattern, or amorphous, with no particular order.
- 💎 Crystalline solids like diamond and graphite demonstrate how different properties arise from the same elemental composition due to different arrangements of atoms.
- 🌐 Crystalline solids are characterized by long-range order, which affects their physical properties and how they change when heated.
- 🔥 Amorphous solids lack long-range order and soften over a range of temperatures, unlike crystalline solids that have a specific melting point.
- 🏺 Examples of amorphous solids include glass, plastic, coal, and rubber, which are more like supercooled liquids.
- 📊 Crystalline structures are built from repeating units called crystal lattices, which dictate the physical properties of the solid.
- 🔬 The unit cell is the smallest repeating unit in a crystal lattice, and different types of unit cells (cubic, hexagonal, etc.) determine the crystal structure.
- 🔄 There are different types of packing in crystals, such as simple cubic, body-centered cubic, and face-centered cubic, each with different coordination numbers.
- 🔬 X-ray diffraction is a technique used to determine the atomic and molecular structure of crystals by analyzing how x-rays scatter off the crystal's atoms.
- 🔑 The arrangement of atoms in a crystalline solid affects properties like atomic coordination numbers, inter-atomic distances, and bonding types.
Q & A
What is the main difference between crystalline and amorphous solids?
-Crystalline solids have a regular repeating three-dimensional structure called a crystal lattice, while amorphous solids have a random orientation of particles with no particular order.
What is the significance of long-range order in crystalline solids?
-Long-range order in crystalline solids refers to the repetition of structural units over long atomic distances, which results in distinct physical properties and behaviors compared to amorphous solids.
How do crystalline solids behave when heated?
-Crystalline solids have a specific melting point where they transition from solid to liquid, and this change in physical properties is sharp and occurs at a specific temperature.
What is the difference between amorphous solids and liquids?
-Amorphous solids are like liquids in that they do not have long-range order, but they have limited localized order in their structure, whereas liquids have no fixed order at all.
Why are crystalline solids considered incompressible?
-Crystalline solids are considered incompressible because their ordered arrangement of units maximizes the space they occupy, and the strong intermolecular forces make them resistant to compression.
What are the common examples of crystalline and amorphous solids mentioned in the script?
-Examples of crystalline solids include ice, sodium chloride, diamond, graphite, and sugar. Amorphous solids include glass, plastic, coal, and rubber.
What are the different types of unit cells in crystalline solids?
-The script mentions seven fundamentally different kinds of unit cells that differ in the relative lengths of the edges and the angles between them. The focus is primarily on cubic unit cells, which include primitive cubic, body-centered cubic, and face-centered cubic.
How does the coordination number in a crystal lattice affect the properties of a material?
-The coordination number, which is the number of atoms or particles surrounding an atom in a crystal lattice, affects atomic coordination numbers, inter-atomic distances, and the types and strengths of bonding within a solid, influencing the physical, chemical, electrical, and mechanical properties of the material.
What is the significance of the crystal lattice in determining the properties of a crystalline solid?
-The crystal lattice is significant because it determines the arrangement of atoms, ions, or molecules in a crystalline solid, which in turn affects the atomic coordination numbers, inter-atomic distances, and bonding types, leading to specific physical and chemical properties.
How is the structure of crystals determined?
-The structure of crystals is determined using X-ray diffraction, a technique that analyzes the patterns formed by the elastic scattering of X-rays off the atoms in a crystal.
What is the Bragg equation and how is it used in X-ray diffraction?
-The Bragg equation, nλ = 2d sinθ, is used in X-ray diffraction to calculate the distance between planes of atoms in a crystal from the angles at which the X-rays are diffracted, where n is an integer, λ is the wavelength of the X-rays, d is the distance between crystal planes, and θ is the angle of incidence.
Outlines
🔬 Introduction to Solids and Their Properties
This paragraph introduces the topic of solids and their properties. The focus is on the distinction between crystalline and amorphous solids. Crystalline solids have a regular, repeating three-dimensional structure known as a crystal lattice, while amorphous solids lack this long-range order and have a random arrangement of particles. Examples of crystalline solids include ice, sodium chloride, diamond, graphite, and sugar, whereas glass, plastic, coal, and rubber are cited as amorphous solids. The difference in properties between these two types of solids stems from the presence or absence of long-range order in their atomic arrangements.
🌡 Behavior of Amorphous Solids Under Heat
The paragraph discusses the behavior of amorphous solids when heated. Unlike crystalline solids, which have a sharp change in physical properties at a specific melting point, amorphous solids soften gradually and melt over a wide range of temperatures. This is due to the random arrangement of particles in their structure, which causes some parts to melt before others. Examples such as coal and plastics illustrate this behavior. The paragraph also introduces the concept of amorphous solids lacking long-range order and having only limited localized order, similar to liquids.
🔬 Crystal Lattice and Unit Cells in Crystalline Solids
This section delves into the concept of the crystal lattice, which is the structural framework of crystalline solids. It explains that the lattice structure depends on the nature and size of the particles involved, as well as the intramolecular and intermolecular forces present. The forces that contribute to the stability of crystalline solids include ionic forces, covalent bonds, metallic bonds, and hydrogen bonds. The paragraph introduces the idea of a unit cell, which is the smallest repeating unit in a crystal lattice, and compares it to a Rubik's cube made up of smaller interconnected cubes. The description also covers the seven fundamental types of unit cells and their characteristics, focusing on cubic unit cells and their properties.
🔍 Types of Cubic Unit Cells and Their Packing
The paragraph explores the different types of cubic unit cells: primitive cubic, body-centered cubic (BCC), and face-centered cubic (FCC). It describes how these unit cells are arranged and the number of particles they contain. The discussion includes the concept of packing, where atoms are arranged to form an ordered three-dimensional structure. The paragraph also explains open and closed packing, with examples of how these packing types appear in different crystalline structures. The coordination number, which is the number of nearest neighbors surrounding a particle in a crystal lattice, is introduced as a key feature of crystal structures.
🔬 Close Packed Lattices and Their Importance
This section discusses close packed lattices, which allow for the maximum amount of interaction between atoms, leading to more energetically stable structures. The paragraph explains the hexagonal close packing (hcp) and face-centered cubic (fcc) or cubic closest packing (ccp) arrangements, detailing how they are formed and their respective unit cell compositions. The importance of understanding atomic packing in a unit cell and crystal lattice is emphasized, as it affects atomic coordination numbers, inter-atomic distances, and the types and strengths of bonding within a solid, which in turn influence the material's physical, chemical, electrical, and mechanical properties.
🔬 Determining Crystal Structures Through X-ray Diffraction
The final paragraph explains how the structures of crystals are determined using x-ray diffraction, a technique that reveals the atomic and molecular structure of a crystal. It describes the process of creating a diffraction pattern by passing x-rays through a powdered crystal sample and how the angles at which the rays are diffracted can be used to calculate the distance between planes of atoms in the crystal. The Bragg equation, which relates the angles of diffraction to the crystal structure, is introduced. The paragraph concludes with a historical note on one of the first x-ray diffraction photographs and a look at modern x-ray diffraction projections.
Mindmap
Keywords
💡Solids
💡Crystalline Solids
💡Amorphous Solids
💡Crystal Lattice
💡Long-range Order
💡Unit Cell
💡Coordination Number
💡Packing
💡X-ray Diffraction
💡Bragg Equation
Highlights
Solids have a rigid structure with component atoms, ions, or molecules usually locked into place.
Crystalline solids are arranged in fixed geometric patterns or lattices, like ice and sodium chloride.
Amorphous solids have a random orientation of particles, such as glass, plastic, coal, and rubber.
More than 90% of naturally occurring and artificially prepared solids are crystalline.
Crystalline solids have long-range order, while amorphous solids lack it.
Crystalline solids become liquids at a specific temperature, known as the melting point.
Amorphous solids soften gradually when heated and can melt over a wide range of temperatures.
Glass is an amorphous solid, composed mainly by mixing molten silicon dioxide with other components.
Crystal lattice is the fundamental concept in solid-state chemistry, representing the smallest structure of a crystal.
There are seven fundamentally different kinds of unit cells that differ in the relative lengths of their edges.
Cubic unit cells are the simplest and have structural particles centered only at their corners.
The arrangement of atoms in a crystalline solid is called packing, which can be open or closed.
The three types of cubic unit cells are primitive cubic, body-centered cubic, and face-centered cubic.
Coordination number is the number of atoms surrounding an atom in a crystal lattice.
Close-packed lattices allow the maximum amount of interaction between atoms, leading to a more stable structure.
Hexagonal closest packing (HCP) and face-centered cubic (FCC) are two common close-packed arrangements.
Understanding atomic packing in a unit cell and crystal lattice can provide insight into the properties of a crystalline material.
X-ray diffraction is a technique used to determine the atomic and molecular structure of a crystal.
The Bragg equation is used to calculate the distance between planes of atoms in a crystal from the angles at which the rays are diffracted.
Transcripts
in this
video we're going to talk about solids
and its properties
the learning competency for this video
is to describe the difference between
the two
and the specific learning outcome is to
compare the properties of crystalline
and
amorphous solids the solid state is
distinguished
from gas and liquid states by a rigid
structure
in which the component atoms ions or
molecules are usually locked
into place in many solids the components
are arranged
in extended three-dimensional patterns
producing a wide range of properties
that can often be tailored to specific
functions
thus a diamond an allotrope of elemental
carbon
is one of the hardest materials known
yet graphite
another allotrope of carbon is a soft
slippery material used in pencil lead
and
as lubricant therefore when we discuss
solids we consider the positions of the
atoms
molecules or ions which are essentially
fixed in space rather than their motions
which are important
in liquids and gases so the constituents
of a solid can be arranged
in two general ways they can form a
regular repeating three-dimensional
structure
called a crystal lattice thus producing
a crystalline solid or they can
aggregate with no particular order
in which case they form an amorphous
solid so it's from the greek word
amorphous
meaning shapeless now the differences in
properties of these two groups
arise from the presence or absence of
long-range order of arrangements
in the solid so what are the differences
crystalline solids are arranged in fixed
geometric patterns or lattices
examples are ice and sodium chloride
other examples include copper sulfate
diamond
graphite and sugar now the ordered
arrangement of their units
maximizes the space they occupy
and are essentially incompressible
amorphous solids on the other hand
have a random orientation of particles
examples include glass plastic
coal and rubber so they are considered
super cooled liquids where molecules
are arranged in a random manner similar
to the liquid state
now more than 90 percent of naturally
occurring and artificially prepared
solids are crystalline minerals
sand clay all have crystalline
structures
now the repetition of structural units
of the substance over long atomic
distances
is referred to as long range order
okay so amorphous solids such as glass
are like liquids they do not have long
range order
but have limited localized order
in their structure so the presence or
absence of
long-range order in the structure of
solids
results in the difference in the
behavior of the solid
when heated okay so as i have said
the structures of crystalline solids are
built from repeating units
called crystal lattices the surroundings
of particles in the structure
are unit form and attractive forces
experienced
by the particles are of similar types
and strands so these attractive forces
are broken by the same
amount of energy and thus crystals
become liquids at a specific
temperature which what we call the
melting point
at the melting point physical properties
of the crystalline solids
change sharply examples are pyrite
or the fool's gold or fluorite
now amorphous solids they soften
gradually when they
are heated they have the tendency to
melt
over a wide range of temperature this
behavior is a result of the variation
in the arrangement of particles in their
structures
causing some parts of the solid to melt
ahead
of other parts this behavior is
noticeable in substances
such as coal and plastics
which are both amorphous solids
so i want to start this discussion with
amorphous solids
because it's easier and less tedious
than crystalline solids amorphous solids
lack
regular arrangement of atoms so we say
that the molecules in an amorphous solid
are
arranged in a random motion
or manner and that we say that this kind
of solid
has no long range further amorphous
solids
also do not diffract glass
is a familiar and important amorphous
solid
they are optically transparent fusion
product of
inorganic materials that has cooled
to a rigid state without crystallization
so glasses are composed mainly by mixing
molten silicon dioxide with other
components such as
sodium oxide boric anhydride and certain
transition
metal oxides so they behave more as a
liquid
than a solid now this figure
shows a crystalline silicon dioxide or
what we call
quartz just by observation
you will already know the difference
between amorphous
silicon dioxide and crystalline
silicon dioxide so what are the
distinguishing feature
of crystalline solids to answer that
we have to further talk about the
crystal lattice
you have to remember that the lattice
structure of a crystal solid
depends on the nature and size of the
particles involved it also depends on
the intramolecular and
intermolecular forces present to be
specific
the force is responsible for the
stability of crystalline solids are the
following
we have ionic forces covalent bonds
thunder valves forces and hydrogen bonds
or a combination of some of them now i
have mentioned
crystal lattice a lot of times but what
exactly
is a crystal lattice
keep in mind that each crystalline solid
is represented by a crystal lattice
now think of crystalline solid as this
rubik's cube
okay so this rubik's cube
is made up of smaller cubes connected
to each other each cube is what we call
a unit cell now the arrangement
or structure of these connected cells
or cubes is what we call a crystal
lattice so basically the crystal lattice
is like a scaffolding for the solid
okay now the unit cell is the
fundamental concept
in solid-state chemistry it is the
smallest representation of structure
which carries all the information
necessary to construct
an ambiguously infinite lattice
okay on a molecular level it looks like
this
so the edge of each unit is what we call
a lattice point
at the lattice point you can see the
atoms
the molecules or ions so this one is a
cubic cell
and it is the simplest unit cell and has
structural particles
centered only at its corners
so if you're going to look at this
figure there are seven fundamentally
different
kinds of unit cells which differ in the
relative
lengths of the edges which are
indicated by a b and c
and the angles between them so alpha is
the angle between b
and c beta is the angle between
a and c and gamma is the angle between
a and b so each unit cell has six
sides and each side is a parallelogram
so we focus primarily on the cubic unit
cells
in which all sides have the same length
and
all angles are 90 degrees but
the concepts that we introduce also
apply to the substances
whose unit cells are not cubic okay
so the way atoms are arranged to form an
ordered three-dimensional structure is
called
packing okay remember that the type of
unit cell is determined
by the way atoms are packed or
arranged in layers so we have two kinds
of packing
open packing and the closed packing by
observation you will see that the open
packing has larger voids in between
particles
compared to close packed crystals
now in some books or references they
call open packing
as square packing because if you notice
you will have four points touching
here one two
three four
okay and they call close packing as
hexagonal packing because you have
six points okay
so you're touching six other atoms
four five six
so we have three types of cubic unit
cells as shown in this figure
we have primitive cubic body centered
cubic
and face centered cubic it's a primitive
cubic when the lattice points
are at the corners only it is a body
centered cubic or bcc when the lattice
point
also occurs at the center of the unit
cell
now it will be called as face centered
cubic or
fcc when the cell has lattice points
at the center of each face as well as
at each corner to make it easier to
visualize i will show you a video
from the user yusuf nasihi
so he makes chemistry physics and other
scientific videos
so if you want you may check his youtube
channel
the video that you will see will discuss
the types of cubic cell
the video the video that you will see
will discuss the types of cubic unit
cells
and their origins okay
if you could travel within a crystalline
solid
you would see the particles atoms ions
or molecules arranged in a regular array
here the spaces are greatly exaggerated
but in reality
the particles are packed close together
the unit cell of a crystal structure is
the smallest
portion that defines the structure
stacking
unit cells next to each other in all
three directions
gives the structure many elements and
simple compounds have unit cells from
the cubic crystal system
let's examine the three types of cubic
unit cells
all cubic unit cells have particles at
the corners of a cube
the simple or primitive cubic unit cell
has particles at the corners
only in reality the particles lie as
close to each other as possible
note that the particles touch along the
cube
edges but not along a diagonal in the
face
or along a diagonal through the body
by slicing away parts that belong to
neighboring unit cells we see that the
actual unit cell consists
of portions of the particles
when the cells pack next to each other
in all three dimensions we obtain the
crystal
if we fade the others out you can see
the original group of eight particles
within the array
and the unit cell within that group we
find the number of particles in one unit
cell by
combining all the particles portions
in the simple cubic unit cell eight
corners
each of which is one eighth of a
particle combine
to give one particle a key feature of a
crystal structure
is its coordination number the number of
the nearest
neighbors surrounding each particle in a
simple cubic array
any given particle has a neighboring
particle above
below to the right to the left in front
and in back of it for a total of
six nearest neighbors the body-centered
cubic unit cell has a particle at each
corner
and one in the center which is colored
pink to make it easier to see
with full size spheres you can see that
the particles don't touch along the
edges of the cube
but each corner particle does touch the
one
in the center the actual unit cell
consists of portions of the corner
particles and the whole one in the
center
eight eighths give one particle and the
one in the center gives
another for a total of two particles
in this tiny portion of a body-centered
cubic array
you can see that any given particle has
four
nearest neighbors above and four below
for a total of eight
nearest neighbors the face-centered
cubic unit cell has a particle at each
corner
and in each face which are colored
yellow here
but none in the center the corner
particles don't touch each other
but each corner does touch a particle in
the face
and those in the faces touch each other
as well
the actual unit cell consists of
portions of particles at the corners
and in the faces eight eighths at the
corners gives one particle
and half a particle in each of six faces
gives
three more for a total of four particles
in this tiny portion of a face-centered
cubic array
notice that a given particle has four
nearest
neighbors around it four more above and
four more below for a total of twelve
nearest neighbors stacking spheres shows
how the three
cubic unit cells arise arrange a layer
of spheres in
horizontal and vertical rows note the
large
diamond-shaped space among the particles
placing the next layer directly over the
first
gives a structure based on the simple
cubic unit cell
those larger spaces mean an inefficient
use of space
in fact only 52 percent of the available
volume
is actually occupied by spheres
because of this inefficiency the simple
cubic unit cell is seen
rarely in nature a more efficient
stacking occurs if we place the second
layer over the spaces formed by the
first layer
and the third layer over the space is
formed by the second
that simple change leads to 68 percent
of the available volume occupied by the
spheres
and a structure based on the body
centered cubic unit cell
many metals including all the alkali
metals adopt
this arrangement for the most efficient
stacking
shift every other row in the first layer
so the large
diamond shaped spaces become smaller
triangular spaces
and place the second layer over them
then the third layer goes over the holes
visible through the first
and second layers in this arrangement
called cubic closest packing spheres
occupy
74 of the volume note that it is based
on the face
centered cubic unit cell okay so again
from the video you have seen the concept
of coordination
number coordination number is the number
of atoms or particles
surrounding an atom in a crystal lattice
or simply the number of atoms touching
it
so coordination numbers indicate how
tightly the atoms pack the larger
coordination numbers
the tighter the packing is so face
centered cubic here has 12
right so now let's talk about the close
packed lattice
in 3d so close packed lattices
allow the maximum amount of interaction
between
atoms so if these interactions
are mainly attractive then close
packing usually leads to a more
energetically
stable structure as we pointed a while
ago
hexagonal packing of a single layer
is more efficient than square packing
so this is where we begin in the first
layer the spheres are arranged
in a hexagonal pattern where each
sphere is being surrounded by six
others okay so we call it layer a
then a second layer b with the same
structure
is added but the layer is slightly
shifted
hence just feeling the gaps off the
first
layer now in a third step another
equivalent
layer is added filling the gaps
just as before but now there are two
opportunities
either this layer lies exactly above the
first
one or so so layer
a again so we'll have a pattern
a b a or it is
shifted with respect to both a
and b and thus has its own
position c so we will have the pattern
c b a this aba pattern is called the
hexagonal closest
backing or hcp while this
cba or abc pattern
is called fcc
or the face centered cubic or some
references they call it ccp
cubic closest back in so let's have a
closer view
this one so a ccp arrangement has a
total of four spheres
per unit cell okay so a ccp
arrangement or a fcc arrangement
has a total of 4 spheres per unit cell
and an hcp arrangement has 8 spheres
per unit cell however both
configurations
have coordination number of wealth
so why is it important to know all of
these
what's the importance of the packing
the arrangement of atoms in a
crystalline solid affects
atomic coordination numbers inter-atomic
distances
and the types and strengths of bonding
that occur
within a solid so an understanding of
atomic packing in a unit cell
and crystal lattice can give insight to
the physical
chemical electrical and mechanical
properties
of a given crystalline material
now we're not going to talk about the
relationship between the edge
length and atomic radius so that would
be for another topic
and for your higher chemistry so how
are the structures of crystals
determined
structures of crystals are determined by
x-ray diffraction x-ray diffraction
is a technique used to determine the
atomic and molecular structure of
a crystal wherein atoms cause beams of
incident x-rays to diffract
into many specific directions
here is an image of a diffraction
pattern
produced by an electron beam incident on
graphite crystal so how does
this work okay so first a sample is
powdered and it is placed
here then x-rays of single wavelength is
used
so from the x-ray tube it will pass
a led screen
then this beam will heat the crystal
sample
diffracting it it means that the wave
scatters
in an elastic manner so we call it
elastic scattering
this is a type of scattering where the
wave
interacting with a particle bounces
off in some direction without changing
its wavelength so this will produce
patterns or spots
from diffracted x-ray okay
now this big circle in the middle is a
spot
from the incident beam that's why you
have here
the shield okay so the distance between
planes of atoms in the crystals
are calculated from the angles at which
the rays are diffracted
using brag equation okay so
here you have two layers okay
layer one and layer two
okay so the incident ray one
will heat atom a and b reflected
at a certain angle so this reflected ray
will be measured by an x-ray detector
okay so and this incident ray 2
will heat atom c then it will be
reflected okay but if you notice
in this figure incident rays
one and two have different path lengths
okay they are only the same
at this point from a to b
and in terms of reflected race it's the
same from
a to d
okay so you have some extra distance
to get the length of the extra distance
s
we need to use some trigonometry
concepts
so from a to c this
will be your hypotenuse d okay
and you will have right angles here
here and angle here
theta so to get the distance from b
to c you will have
d sine theta
and from c to d you will have
d sine
theta so the extra distance
traveled by the lower ray is equal to
bc plus cd
which is equal to n
times lambda where n
is an integer and lambda is the
wavelength of the x-rays
so this will be equal to
2 d sine
theta okay so this
is what we call the bragg equation
now i'm going to leave the solving part
to your higher chem subjects
but this is one of the ways to derive
brag
equation this figure shows one of the
first
x-ray diffraction photographs so the
figure on the left
is one of the first x-ray diffraction
photograph
and on the right is a modern x-ray
diffraction
projection okay so in the next video
we're going to talk about the types of
crystals
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