Chemistry lessin 7.3 ppt

ppt

1. 7.3 Bonding in Metals >
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Chapter 7
Ionic and Metallic Bonding
7.1 Ions
7.2 Ionic Bonds and
Ionic Compounds
7.3 Bonding in Metals

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CHEMISTRY&YOU
What are some properties that are
unique to metals?
Wrought iron is a very
pure form of iron that
contains trace
amounts of carbon. It
is a tough, malleable,
ductile, and corrosion-
resistant material that
melts at very high
temperatures.

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Metallic Bonds and Metallic
Properties
Metallic Bonds and Metallic Properties
How can you model the valence
electrons of metal atoms?

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Metallic Bonds and Metallic
Properties
Metallic Bonds and Metallic Properties
How can you model the valence
electrons of metal atoms?
•Metals consist of closely packed
cations and loosely held valence
electrons rather than neutral atoms.
[Answer to Question 1]

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Metallic Bonds and Metallic
Properties
The valence electrons of atoms in a
pure metal can be modeled as a sea
of electrons.

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Metallic Bonds and Metallic
Properties
The valence electrons of atoms in a
pure metal can be modeled as a
sea of electrons.
•The valence electrons are mobile and
can drift freely from one part of the
metal to another.
[Answer to Question 2]
[Answer to Question 3]

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Metallic Bonds and Metallic
Properties
Metallic bondsare the forces of
attraction between the free-floating
valence electrons and the positively
charged metal ions.
•These bonds hold metals together.
[Answer to Question 4]

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Metallic Bonds and Metallic
Properties
Properties of Metals
Metals are good conductors of electric
current because electrons can flow
freely in the metal.

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Metallic Bonds and Metallic
Properties
Properties of Metals
Metals are good conductors of
electric current because electrons
can flow freely in the metal.
•As electrons enter one end of a bar of
metal, an equal number of electrons leave
the other end.
[Answer to Question 5]
[Answer to Question 6]

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Metallic Bonds and Metallic
Properties
Metals are ductile—that is, they can be
drawn into wires.
Properties of Metals
Force
Metal
rod
Die
Wire

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Metallic Bonds and Metallic
Properties
Metals are ductile—that is, they can
be drawn into wires.
•Metals are also
malleable, which
means that they
can be hammered
or pressed into
shapes.
Properties of Metals
Force
Metal
rod
Die
Wire
[Answer to Question 7]
[Answer to Question 8]

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Metallic Bonds and Metallic
Properties
When a metal is subjected to pressure, the
metal cations easily slide past one another.
Properties of Metals
Sea of
electrons
Metal
cation
Force
Metal

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Metallic Bonds and Metallic
Properties
When a metal is subjected to pressure, the
metal cations easily slide past one another.
•If an ionic crystal is struck
with a hammer, the blow
tends to push the positive
ions close together.
•The positive ions repel
one another, and the
crystal shatters.
Properties of Metals
Sea of
electrons
Metal
cation
Force Force
Metal
cation
Strong
repulsions
Nonmetal
anion
Metal Ionic crystal

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How are metals and ionic compounds
different? How are they similar?
CHEMISTRY&YOU

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How are metals and ionic compounds
different? How are they similar?
CHEMISTRY&YOU
Both metals and ionic compounds
form crystal structures. However, they
have different configurations of
electrons. The sea of electrons
surrounding cations in a metal allows
metals to be ductile and malleable.
Ionic crystals will fracture under
pressure.
[Answer to Question 9]

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Metallic Bonds and Metallic
Properties
Crystalline Structure of Metals
For spheres of identical size, such as metal atoms,
several closely packed arrangements are possible.
•These Thai oranges illustrate
a pattern called a hexagonal
close-packed
arrangement.

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Metallic Bonds and Metallic
Properties
Crystalline Structure of Metals
In a body-centered cubic structure, every atom
(except those on the surface) has eight neighbors.
•The metallic
elements sodium,
potassium, iron,
chromium, and
tungsten crystallize
in a body-centered
cubic pattern.
Chromium

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Metallic Bonds and Metallic
Properties
Crystalline Structure of Metals
In a face-centered cubic arrangement, every atom
has twelve neighbors.
•Among the metals
that form a face-
centered cubic
structure are copper,
silver, gold,
aluminum, and lead.
Gold

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Metallic Bonds and Metallic
Properties
Crystalline Structure of Metals
In a hexagonal close-packed arrangement, every
atom also has twelve neighbors.
•Metals that have a
hexagonal close-
packed crystal
structure include
magnesium, zinc, and
cadmium.
Zinc
•The pattern is different from the
face-centered cubic arrangement.

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Which of the following models can
describe the valence electrons of metals?
A.A body-centered cube
B.Octets of electrons
C.A rigid array of electrons
D.A sea of electrons

21. 7.3 Bonding in Metals >
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Which of the following models can
describe the valence electrons of metals?
A.A body-centered cube
B.Octets of electrons
C.A rigid array of electrons
D.A sea of electrons

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Alloys
Alloys
Why are alloys important?

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Alloys
Alloys
Why are alloys important?
•Alloysare mixtures of two or more
elements, at least one of which is a metal.
–Brass, for example, is an alloy of copper
and zinc.
[Answer to Question 10]

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Alloys
Alloys are important because
their properties are often
superior to those of their
component elements.
[Answer to Question 11]

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Alloys
Alloys are important because their
properties are often superior to
those of their component elements.
•Sterling silver (92.5 percent
silver and 7.5 percent
copper) is harder and more
durable than pure silver, yet
it is still soft enough to be
made into jewelry and
tableware.

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Alloys
The most important alloys today are
steels.
•The principal elements in most steels, in addition to
iron and carbon, are boron, chromium, manganese,
molybdenum, nickel,
tungsten, and vanadium.
•Steels have a wide
range of useful
properties, such as
corrosion resistance,
ductility, hardness, and
toughness.
Stainless Steel
80.6% Fe
18.0% Cr
0.4% C
1.0% Ni
[Answer to Question 12]

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Alloys
Alloys can form from their component
atoms in different ways.

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Alloys
Alloys can form from their component
atoms in different ways.
•If the atoms of the components in an alloy are
about the same size, they can replace each
other in the crystal.
–This type of alloy is called a substitutional alloy.

29. 7.3 Bonding in Metals >
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Alloys
Alloys can form from their component
atoms in different ways.
•If the atoms of the components in an alloy are
about the same size, they can replace each
other in the crystal.
–This type of alloy is called a substitutional alloy.
•If the atomic sizes are quite different, the
smaller atoms can fit into the interstices
(spaces) between the larger atoms.
–Such an alloy is called an interstitial alloy.

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Explain why alloys are important, and
list one important alloy.

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Explain why alloys are important, and
list one important alloy.
Alloys are important because they often
have properties that are superior to those of
the elements from which they are made.
Stainless steel is an important alloy because
of its corrosion resistance.
[Answer to Question 13]

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Key Concepts
The valence electrons of atoms in a
pure metal can be modeled as a sea of
electrons.
Alloys are important because their
properties are often superior to those
of their component elements.

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Glossary Terms
•metallic bond: the force of attraction that
holds metals together; it consists of the
attraction of free-floating valence electrons for
positively charged metal ions
•alloy: a mixture composed of two or more
elements, at least one of which is a metal

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•Metals are made up of closely packed
cations surrounded by a sea of
electrons.
•The sea-of-electrons model explains
why metals are good conductors of
electric current and why they are ductile
and malleable.
BIGIDEA
Bonding and Interactions

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END OF 7.3