Transcript 13.3 The Nature of Solids

13.3 The Nature of Solids >
Chapter 13
States of Matter
13.1 The Nature of Gases
13.2 The Nature of Liquids
13.3 The Nature of Solids
13.4 Changes of State
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13.3 The Nature of Solids >
CHEMISTRY
& YOU
What is the strongest material in the
world?
It’s not steel or
any synthetic
plastic, but a form
of pure carbon
known as fullerene
nanotubes.
2
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13.3 The Nature of Solids > A Model for Solids
A Model for Solids
How are the structure and properties
of solids related?
3
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13.3 The Nature of Solids > A Model for Solids
The general properties of solids reflect
the orderly arrangement of their particles
and the fixed locations of their particles.
4
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13.3 The Nature of Solids > A Model for Solids
The general properties of solids reflect
the orderly arrangement of their particles
and the fixed locations of their particles.
• In most solids, the atoms, ions, or molecules
are packed tightly together.
5
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13.3 The Nature of Solids > A Model for Solids
The general properties of solids reflect
the orderly arrangement of their particles
and the fixed locations of their particles.
• In most solids, the atoms, ions, or molecules
are packed tightly together.
• Solids are dense and not easy to compress.
6
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13.3 The Nature of Solids > A Model for Solids
The general properties of solids reflect
the orderly arrangement of their particles
and the fixed locations of their particles.
• In most solids, the atoms, ions, or molecules
are packed tightly together.
• Solids are dense and not easy to compress.
• Because the particles in solids tend to vibrate
about fixed points, solids do not flow.
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13.3 The Nature of Solids > A Model for Solids
When you heat a solid, its particles vibrate
more rapidly as their kinetic energy
increases.
• The melting point (mp) is the temperature
at which a solid changes into a liquid.
8
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13.3 The Nature of Solids > A Model for Solids
When you heat a solid, its particles vibrate
more rapidly as their kinetic energy
increases.
• The melting point (mp) is the temperature
at which a solid changes into a liquid.
– At this temperature, the disruptive
vibrations of the particles are strong
enough to overcome the attractions that
hold them in fixed positions.
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13.3 The Nature of Solids > A Model for Solids
The freezing point (fp) is the temperature
at which a liquid changes into a solid.
• The melting and freezing points of a
substance are at the same temperature.
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13.3 The Nature of Solids > A Model for Solids
The freezing point (fp) is the temperature
at which a liquid changes into a solid.
• The melting and freezing points of a
substance are at the same temperature.
• At that temperature, the liquid and solid
phases are in equilibrium.
Solid
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melting
freezing
Liquid
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13.3 The Nature of Solids > A Model for Solids
• In general, ionic solids have high melting
points because relatively strong forces hold
them together.
– Sodium chloride, an ionic compound,
has a rather high melting point of
801°C.
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13.3 The Nature of Solids > A Model for Solids
• In general, ionic solids have high melting
points because relatively strong forces hold
them together.
– Sodium chloride, an ionic compound,
has a rather high melting point of
801°C.
• Molecular solids have relatively low melting
points.
– Hydrogen chloride, a molecular
compound, melts at –112°C.
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13.3 The Nature of Solids >
Explain why solids do not flow, even
though their particles are constantly
moving.
14
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13.3 The Nature of Solids >
Explain why solids do not flow, even
though their particles are constantly
moving.
In a solid, the particles are packed tightly
together and vibrate around fixed points.
Even though the particles vibrate, they are
limited in their movement and cannot flow.
15
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13.3 The Nature of Solids > Crystal Structure and
Unit Cells
Crystal Structure and Unit Cells
What determines the shape of a
crystal?
16
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13.3 The Nature of Solids > Crystal Structure and
Unit Cells
Crystal Structure and Unit Cells
What determines the shape of a
crystal?
• In a crystal, the particles are arranged in
an orderly, repeating, three-dimensional
pattern called a crystal lattice.
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13.3 The Nature of Solids > Crystal Structure and
Unit Cells
The shape of a crystal reflects the
arrangement of the particles within
the solid.
• In sodium chloride,
sodium ions and
chloride ions are closely
packed in a regular
array.
• The ions vibrate about
fixed points in the
crystal.
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13.3 The Nature of Solids > Crystal Structure and
Unit Cells
Crystal Systems
Crystals are classified into seven groups,
or crystal systems.
c
c
c
a
b
c
a
b
a=b=c
a=b≠c
o
a = b = g = 90 a = b = g = 90o
Cubic
Tetragonal
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a
a≠b≠c
a = b = g = 90o
Orthorhombic
b
b
a
a≠b≠c
b = g = 90o ≠ a
Monoclinic
c
c
a
b
a≠b≠c
a ≠ b ≠ g ≠ 90o
Triclinic
c
a
b
a=b≠c
a = b = 90o, g = 120o
Hexagonal
a
b
a=b=c
a = b = g ≠ 90o
Rhombohedral
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13.3 The Nature of Solids > Crystal Structure and
Unit Cells
Crystal Systems
c
c
c
a
b
c
a
b
a=b=c
a=b≠c
o
a = b = g = 90 a = b = g = 90o
Cubic
Tetragonal
a
a≠b≠c
a = b = g = 90o
Orthorhombic
b
b
a
a≠b≠c
b = g = 90o ≠ a
Monoclinic
c
c
a
c
b
a≠b≠c
a ≠ b ≠ g ≠ 90o
Triclinic
a
b
a=b≠c
a = b = 90o, g = 120o
Hexagonal
a
a=b=c
a = b = g ≠ 90o
Rhombohedral
• The edges are labeled a, b, and c.
• The angles are labeled α, β, and γ.
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b
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13.3 The Nature of Solids > Crystal Structure and
Unit Cells
Crystal Systems
c
c
c
a
b
c
a
b
a=b=c
a=b≠c
o
a = b = g = 90 a = b = g = 90o
Cubic
Tetragonal
a
a≠b≠c
a = b = g = 90o
Orthorhombic
b
b
a
a≠b≠c
b = g = 90o ≠ a
Monoclinic
c
c
a
b
a≠b≠c
a ≠ b ≠ g ≠ 90o
Triclinic
c
a
b
a=b≠c
a = b = 90o, g = 120o
Hexagonal
a
a=b=c
a = b = g ≠ 90o
Rhombohedral
The seven crystal systems differ in terms of the
angles between the faces and in the number of
edges of equal length on each face.
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b
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13.3 The Nature of Solids > Crystal Structure and
Unit Cells
Crystal Systems
The shape of a crystal depends on the
arrangement of particles within it.
• The smallest group of particles within a
crystal that retains the geometric shape of
the crystal is known as a unit cell.
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13.3 The Nature of Solids > Crystal Structure and
Unit Cells
Crystal Systems
A crystal lattice is a repeating array of
any one of fourteen kinds of unit cells.
• Each crystal system can be composed of
from one to four types of unit cells.
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13.3 The Nature of Solids > Crystal Structure and
Unit Cells
Crystal Systems
The figure below shows the three kinds of unit
cells that can make up a cubic crystal system.
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Simple Cubic
Body-Centered
Face-Centered
In a simple cubic unit cell,
atoms or ions are
arranged at the corners
of an imaginary cube.
In a body-centered cubic unit
cell, the atoms or ions are at
the corners and in the center
of an imaginary cube.
In a face-centered cubic unit cell,
there are atoms or ions at the
corners and in the center of each
face of an imaginary cube.
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13.3 The Nature of Solids > Crystal Structure and
Unit Cells
Allotropes
Some substances can exist in more than
one form.
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13.3 The Nature of Solids > Crystal Structure and
Unit Cells
Allotropes
Some substances can exist in more than
one form.
• Diamond is one crystalline form of carbon.
• A different form of carbon is graphite.
• In 1985, a third crystalline form of carbon
was discovered. This form is called
buckminsterfullerene.
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13.3 The Nature of Solids > Crystal Structure and
Unit Cells
Allotropes
In diamond, each
carbon atom in the
interior of the
diamond is strongly
bonded to four
others. The array is
rigid and compact.
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In graphite, the
carbon atoms are
linked in widely
spaced layers of
hexagonal
arrays.
In buckminsterfullerene, 60 carbon
atoms form a hollow
sphere. The
carbons are
arranged in pentagons and hexagons.
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13.3 The Nature of Solids > Crystal Structure and
Unit Cells
Allotropes
The physical properties of diamond,
graphite, and fullerenes are quite different.
• Diamond has a high density and is very
hard.
• Graphite has a relatively low density and is
soft and slippery.
• The hollow cages in fullerenes give them
strength and rigidity.
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13.3 The Nature of Solids > Crystal Structure and
Unit Cells
Allotropes
Diamond, graphite, and fullerenes are
crystalline allotropes of carbon.
• Allotropes are two or more different
molecular forms of the same element in the
same physical state.
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13.3 The Nature of Solids > Crystal Structure and
Unit Cells
Allotropes
Diamond, graphite, and fullerenes are
crystalline allotropes of carbon.
• Allotropes are two or more different
molecular forms of the same element in the
same physical state.
• Although allotropes are composed of atoms
of the same element, they have different
properties because their structures are
different.
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13.3 The Nature of Solids > Crystal Structure and
Unit Cells
Allotropes
Only a few elements have allotropes.
• In addition to carbon, these include
phosphorus, sulfur, oxygen (O2 and O3),
boron, and antimony.
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13.3 The Nature of Solids >
CHEMISTRY
& YOU
What structural properties
make fullerene nanotubes the
strongest material in the
world?
32
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13.3 The Nature of Solids >
CHEMISTRY
& YOU
What structural properties
make fullerene nanotubes the
strongest material in the
world?
Each carbon atom is covalently bonded to three
other carbon atoms. The structure creates a
spherical cage or cylindrical tube. This shape
allows force to be distributed evenly across the
surface so that the entire structure can
withstand great force and is extremely strong.
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13.3 The Nature of Solids > Crystal Structure and
Unit Cells
Non-Crystalline Solids
Not all solids are crystalline in form; some
solids are amorphous.
• An amorphous solid lacks an ordered
internal structure.
• Rubber, plastic, and asphalt are amorphous
solids.
• Their atoms are randomly arranged.
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13.3 The Nature of Solids > Crystal Structure and
Unit Cells
Non-Crystalline Solids
Other examples of amorphous solids are glasses.
• A glass is a transparent fusion product of
inorganic substances that have cooled to a
rigid state without crystallizing.
• Glasses are sometimes called supercooled
liquids.
• The irregular internal structures are
intermediate between those of a crystalline
solid and those of a free-flowing liquid.
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13.3 The Nature of Solids >
What is the difference between an
amorphous solid and a crystalline
solid?
36
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13.3 The Nature of Solids >
What is the difference between an
amorphous solid and a crystalline
solid?
Particles in a crystalline solid are arranged in
an orderly, repeating pattern or lattice.
Particles in an amorphous solid are arranged
randomly.
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13.3 The Nature of Solids > Key Concepts
The general properties of solids reflect the
orderly arrangement and the fixed locations
of their particles.
The shape of a crystal reflects the
arrangement of the particles within the
solid.
38
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13.3 The Nature of Solids > Glossary Terms
• melting point: the temperature at which a
substance changes from a solid to a liquid; the
melting point of water is 0°C
• freezing point: the temperature at which a
liquid changes into a solid
• crystal: a solid in which the atoms, ions, or
molecules are arranged in an orderly,
repeating, three-dimensional pattern called a
crystal lattice
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13.3 The Nature of Solids > Glossary Terms
• unit cell: the smallest group of particles within
a crystal that retains the geometric shape of
the crystal
• allotrope: one of two or more different
molecular forms of an element in the same
physical state; oxygen (O2) and ozone (O3) are
allotropes of the element oxygen
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13.3 The Nature of Solids > Glossary Terms
• amorphous solid: describes a solid that lacks
an ordered internal structure; denotes a
random arrangement of atoms
• glass: a transparent fusion product of
inorganic substances that have cooled to a
rigid state without crystallizing
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13.3 The Nature of Solids >
END OF 13.3
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