properties of solids. copyright © pearson education, inc., or its affiliates. all rights reserved....

Properties of Solids

Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

•What is the strongest material in the world?

CHEMISTRY & YOUCHEMISTRY & YOU

It’s not steel or any synthetic plastic, but a form of pure carbon known as fullerene nanotubes.


A Model for Solids

• 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.

The general properties of solids reflect the orderly arrangement of their particles and the fixed locations of their particles.


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.


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 Liquidmelting

freezing


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.


•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.


Crystal Structure and Unit Cells

• Crystal Structure and Unit Cells

• In a crystal, the particles are arranged in an orderly, repeating, three-dimensional pattern called a crystal lattice.

What determines the shape of a crystal?



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.



• Crystal Systems

Crystals are classified into seven groups, or crystal systems.

a = b = c

a = b = g = 90o

Cubic

a = b ≠ c

a = b = g = 90o

Tetragonal

a ≠ b ≠ c

a = b = g = 90o

Orthorhombic

a ≠ b ≠ c

b = g = 90o ≠ aMonoclinic

a ≠ b ≠ c

a ≠ b ≠ g ≠ 90o

Triclinic

a a a a a a ab b b b b b

c

c

cc c

c

c

b

a = b ≠ c

a = b = 90o, g = 120o

Hexagonal

a = b = c

a = b = g ≠ 90o

Rhombohedral



• Crystal Systems

• The edges are labeled a, b, and c.

• The angles are labeled α, β, and γ.

a = b = c

a = b = g = 90o

Cubic

a = b ≠ c

a = b = g = 90o

Tetragonal

a ≠ b ≠ c

a = b = g = 90o

Orthorhombic

a ≠ b ≠ c


a ≠ b ≠ c

a ≠ b ≠ g ≠ 90o

Triclinic


c

c

cc c

c

c

b

a = b ≠ c

a = b = 90o, g = 120o

Hexagonal

a = b = c

a = b = g ≠ 90o

Rhombohedral



• Crystal Systems

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.

a = b = c

a = b = g = 90o

Cubic

a = b ≠ c

a = b = g = 90o

Tetragonal

a ≠ b ≠ c

a = b = g = 90o

Orthorhombic

a ≠ b ≠ c


a ≠ b ≠ c

a ≠ b ≠ g ≠ 90o

Triclinic


c

c

cc c

c

c

b

a = b ≠ c

a = b = 90o, g = 120o

Hexagonal

a = b = c

a = b = g ≠ 90o

Rhombohedral



• 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.



• 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.



• Crystal SystemsThe figure below shows the three kinds of unit cells that can make up a cubic crystal system.

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.



• Allotropes

Some substances can exist in more than one form.



• 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.



• Allotropes

In diamond, each carbon atom in the interior of the diamond is strongly bonded to four others. The array is rigid and compact.

In graphite, the carbon atoms are linked in widely spaced layers of hexagonal arrays.

In buckminster-fullerene, 60 carbon atoms form a hollow sphere. The carbons are arranged in penta-gons and hexagons.



• 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.



• 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.



• Allotropes

Only a few elements have allotropes.

• In addition to carbon, these include phosphorus, sulfur, oxygen (O2 and O3), boron, and antimony.


•What structural properties make fullerene nanotubes the strongest material in the world?



•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.




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.

• Non-Crystalline Solids



• 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.


•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.


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.


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


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


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

properties of solids. copyright © pearson education, inc., or its affiliates. all rights reserved....

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