7.1 Ions >
Chapter 7
Ionic and Metallic Bonding
7.1 Ions
7.2 Ionic Bonds and
Ionic Compounds
7.3 Bonding in Metals
1
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7.1 Ions > Valence Electrons
Valence electrons are the electrons in
the highest occupied energy level of an
element’s atoms.
• The number of valence electrons largely
determines the chemical properties of an
element.
2
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7.1 Ions > Valence Electrons
Determining the Number of Valence
Electrons
To find the number of valence
electrons in an atom of a
representative element, simply look
at its group number.
3
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7.1 Ions > Valence Electrons
Determining the Number of Valence
Electrons
• Atoms of the Group 1A elements (hydrogen, lithium,
sodium, and so forth) all have one valence electron,
corresponding to the 1 in 1A.
• Carbon and silicon atoms, in Group 4A, have four
valence electrons.
• The noble gases (Group 8A) are the only exceptions to
the group-number rule: Atoms of helium have two
valence electrons, and atoms of all the other noble
gases have eight valence electrons.
4
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7.1 Ions > Valence Electrons
Determining the Number of Valence
Electrons
Valence electrons are usually the only
electrons involved in chemical bonds.
• As a general rule, only the valence electrons are
shown in electron dot structures.
• Electron dot structures are diagrams that
show valence electrons in the atoms of an
element as dots.
5
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7.1 Ions >
Interpret Data
Electron Dot Structures of Some Group A Elements
Group
Period
1A
2A
3A
4A
5A
6A
7A
8A
1
2
3
4
This table shows electron dot structures for atoms
of some Group A elements.
• Notice that all the electrons within a given group (with
the exception of helium) have the same number of
electron dots in their structures.
6
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7.1 Ions > Valence Electrons
The Octet Rule
Noble gases, such as neon and argon, are
nonreactive in chemical reactions.
• That is, they are stable.
• In 1916, chemist Gilbert Lewis used this fact to
explain why atoms form certain kinds of ions
and molecules.
• He called his explanation the octet rule.
7
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7.1 Ions > Valence Electrons
The Octet Rule
The octet rule states that in forming
compounds, atoms tend to achieve the
electron configuration of a noble gas.
• An octet is a set of eight.
• Atoms of each of the noble gases (except
helium) have eight electrons in their highest
occupied energy levels and the general
electron configuration of ns2np6.
8
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7.1 Ions > Valence Electrons
The Octet Rule
• Atoms of metals tend to lose their valence
electrons, leaving a complete octet in the
next-lowest energy level.
• Atoms of some nonmetals tend to gain
electrons or share electrons with another
nonmetal atom or atoms to achieve a
complete octet.
9
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7.1 Ions > Formation of Cations
Formation of Cations
How are cations formed?
• An atom is electrically neutral because it has
equal numbers of protons and electrons.
• An ion forms when an atom or group of atoms
loses or gains electrons.
10
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7.1 Ions > Formation of Cations
A positively charged ion, or cation, is
produced when an atom loses one or
more valence electrons.
• A sodium atom (Na) forms a sodium cation
(Na+).
• A calcium atom (Ca) forms a calcium
cation (Ca+).
11
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7.1 Ions > Formation of Cations
Group 1A Cations
The most common cations are those
produced by the loss of valence electrons
from metal atoms.
• Most of these atoms have one to three valence
electrons, which are easily removed.
12
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7.1 Ions > Formation of Cations
Group 1A Cations
When forming a compound, a sodium atom
loses its one valence electron and is left
with an octet in what is now its highest
occupied energy level.
• The number of protons in the sodium nucleus is
still eleven, so the loss of one unit of negative
charge produces a cation with a charge of 1+.
Na
–e–
2
2
6
1
1s 2s 2p 3s
Na+ 1s22s22p6
octet
13
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7.1 Ions > Formation of Cations
Group 1A Cations
Both the sodium ion and the neon atom have
eight electrons in their valence shells (highest
occupied energy levels).
14
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7.1 Ions > Formation of Cations
Group 2A Cations
Magnesium (atomic number 12) belongs to
Group 2A of the periodic table, so magnesium
atoms have two valence electrons.
• A magnesium atom attains the electron
configuration of a neon atom by losing both
valence electrons and producing a
magnesium cation with a charge of 2+.
• Mg •
loses all its
valence
electrons
Magnesium atom
(electrically neutral,
charge = 0)
15
Mg2+
Magnesium ion (2+
indicates two units
of positive charge)
+
2e–
(2 in front of e–
indicates two units of
negative charge)
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7.1 Ions > Formation of Cations
The figure at right lists the symbols of the
cations formed by metals
in Groups 1A and 2A.
• Cations of Group 1A
elements always have
a charge of 1+.
• Cations of Group 2A
elements always have
a charge of 2+.
16
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7.1 Ions > Formation of Cations
Transition Metal Cations
The charges of cations of the transition
metals may vary.
• An atom of iron may lose two valence
electrons, forming the Fe2+ cation, or three
valence electrons, forming the Fe3+ cation.
17
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7.1 Ions > Formation of Cations
Transition Metal Cations
Some ions formed by transition metals do not
have noble-gas electron configurations (ns2np6)
and are therefore exceptions to the octet rule.
• Silver, with the electron configuration of
1s22s22p63s22p63d104s24p64d105s1, is an example.
• To achieve the structure of krypton, a silver atom would
have to lose eleven electrons.
• To acquire the electron configuration of xenon, a silver
atom would have to gain seven electrons.
• Ions with charges of three or greater are uncommon.
18
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7.1 Ions > Formation of Cations
Transition Metal Cations
A copper atom loses its lone 4s electron to form a copper
ion (Cu+) with a pseudo noble-gas electron configuration,
as illustrated below.
19
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7.1 Ions >
CHEMISTRY
& YOU
Fool’s gold is composed of iron(II)
cations (Fe2+) and disulfide anions
(S22–). Write the electron configuration
of the Fe2+ ion.
Fe: 1s22s22p63s23p63d64s2
Fe2+: 1s22s22p63s23p63d6
20
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7.1 Ions >
How does a cesium atom form a cation?
A. By losing 2 electrons
B. By gaining 1 electron
C. By losing 1 electron
D. By gaining 2 electrons
21
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7.1 Ions > Formation of Anions
An anion is produced when an
atom gains one or more valence
electrons.
• Note that the name of an anion of a
nonmetallic element is not the same as
the element name.
– The name of the anion typically ends in -ide.
– Thus, a chlorine atom (Cl) forms a chloride
anion (Cl–).
– An oxygen atom (O) forms an oxide anion (O2–).
22
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7.1 Ions > Formation of Anions
Atoms of nonmetals and
metalloids form anions
by gaining enough
valence electrons to
attain the electron
configuration of the
nearest noble gas.
23
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7.1 Ions > Formation of Anions
Atoms of nonmetallic elements attain noble-gas
electron configurations more easily by gaining
electrons than by losing them because these
atoms have relatively full valence shells.
• Atoms of chlorine have seven valence
electrons.
– A gain of one electron gives a chlorine atom an
octet and converts a chlorine atom into a
chloride atom.
Cl
1s22s22p63s23p5
+e–
Cl– 1s22s22p63s23p6
octet
24
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7.1 Ions > Formation of Anions
Chlorine atoms need one more valence electron
to achieve the electron configuration of the
nearest noble gas.
25
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7.1 Ions > Formation of Anions
The ions produced when atoms of chlorine and
other halogens gain electrons are called halide
ions.
• All halogen atoms have seven valence
electrons and need to gain only one electron
to achieve the electron configuration of a
noble gas.
– All halide ions (F–, Cl–, Br–, and I–) have a
charge of 1–.
26
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7.1 Ions > Formation of Anions
Oxygen is in Group 6A, and an oxygen atom has
six valence electrons.
• An oxygen atom attains the electron configuration of
neon by gaining two electrons.
27
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7.1 Ions >
Interpret Data
This table lists
some common
anions.
28
Some Common Anions
Name
Symbol
Charge
Fluoride
F–
1–
Chloride
Cl–
1–
Bromide
Br–
1–
Iodide
I–
1–
Oxide
O2–
2–
Sulfide
S2–
2–
Nitride
N3–
3–
Phosphide
P3–
3–
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7.1 Ions >
What is the electron configuration of a
sulfide ion? What noble gas shares
this configuration?
S2–: 1s22s22p63s23p6
This is the same configuration as Ar.
29
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7.1 Ions > Key Concepts
To find the number of valence electrons in
an atom of a representative element,
simply look at its group number.
A positively charged ion, or cation, is
produced when an atom loses one or more
valence electrons.
An anion is produced when an atom gains
one or more valence electrons.
30
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7.1 Ions > Glossary Terms
• valence electron: an electron in the highest
occupied energy level of an atom
• electron dot structure: a notation that depicts
valence electrons as dots around the atomic
symbol of the element; the symbol represents
the inner electrons and atomic nucleus; also
called Lewis dot structure
31
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7.1 Ions > Glossary Terms
• octet rule: atoms react by gaining or losing
electrons so as to acquire the stable electron
structure of a noble gas, usually eight valence
electrons
• halide ion: a negative ion formed when a
halogen atom gains an electron
32
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7.1 Ions >
BIG IDEA
Bonding and Interactions
Atoms form positive ions (cations) by
losing valence electrons and form
negative ions (anions) by gaining
valence electrons.
33
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7.1 Ions >
Chapter 7
Ionic and Metallic Bonding
7.1 Ions
7.2 Ionic Bonds and
Ionic Compounds
7.3 Bonding in Metals
34
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7.1 Ions >
CHEMISTRY
& YOU
Where does table salt come from?
In some countries,
salt is obtained by
the evaporation of
seawater. In other
countries, salt is
mined from rock
deposits deep
underground.
35
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7.1 Ions > Formation of Ionic Compounds
Sodium chloride, or table salt, is an ionic
compound consisting of sodium cations
and chloride anions.
• An ionic compound is a compound
composed of cations and anions.
36
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7.1 Ions > Formation of Ionic Compounds
Although they are composed of ions,
ionic compounds are electrically
neutral.
• The total positive charge of the
cations equals the total negative
charge of the anions.
37
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7.1 Ions > Formation of Ionic Compounds
Ionic Bonds
Anions and cations have opposite charges
and attract one another by means of
electrostatic forces.
• The electrostatic forces that hold ions
together in ionic compounds are called
ionic bonds.
38
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7.1 Ions > Formation of Ionic Compounds
Ionic Bonds
When sodium and chlorine react to form a
compound, the sodium atom transfers its one
valence electron to the chlorine atom.
• Sodium and chlorine atoms combine in a one-toone ratio, and both ions have stable octets.
39
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7.1 Ions > Formation of Ionic Compounds
Ionic Bonds
Aluminum metal (Al) and
the nonmetal bromine (Br2)
react violently to form the
ionic solid aluminum
bromide (AlBr3).
• Each bromine atom has seven
valence electrons and readily
gains one additional electron.
• Three bromine atoms
combine with each aluminum
atom.
40
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7.1 Ions > Formation of Ionic Compounds
Formula Units
A chemical formula shows the
numbers of atoms of each element in
the smallest representative unit of a
substance.
• NaCl is the chemical formula for sodium
chloride.
41
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7.1 Ions > Formation of Ionic Compounds
Formula Units
Ionic compounds do not exist as discrete units, but as
collections of positively and negatively charged ions
arranged in repeating patterns.
42
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7.1 Ions > Formation of Ionic Compounds
Formula Units
The chemical formula of an ionic
compound refers to a ratio known as a
formula unit.
• A formula unit is the lowest wholenumber ratio of ions in an ionic compound.
43
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7.1 Ions > Formation of Ionic Compounds
Formula Units
For sodium chloride, the lowest wholenumber ratio of the ions is 1:1 (one
Na+ ion to each Cl– ion).
• The formula unit for sodium chloride is NaCl.
• Although ionic charges are used to derive the
correct formula, they are not shown when
you write the formula unit of the compound.
44
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7.1 Ions >
Sample Problem 7.1
Predicting Formulas of Ionic Compounds
Use electron dot structures to
predict the formulas of the ionic
compounds formed from the
following elements:
a. potassium and oxygen
b. magnesium and nitrogen
45
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7.1 Ions >
Sample Problem 7.1
1 Analyze Identify the relevant concepts.
• Atoms of metals lose valence electrons
when forming an ionic compound.
• Atoms of nonmetals gain electrons.
• Enough atoms of each element must be
used in the formula so that electrons lost
equal electrons gained.
46
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7.1 Ions >
Use electron dot structures to
determine the formula of the ionic
compound formed when calcium
reacts with fluorine.
47
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7.1 Ions > Properties of Ionic Compounds
Properties of Ionic Compounds
What are three properties of
ionic compounds?
48
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7.1 Ions > Properties of Ionic Compounds
Most ionic compounds are crystalline
solids at room temperature.
• The component ions in such crystals
are arranged in repeating threedimensional patterns.
The beauty of
crystalline solids
comes from the
orderly arrangement of
their component ions.
49
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7.1 Ions > Properties of Ionic Compounds
Each ion is attracted strongly to each of its
neighbors, and repulsions are minimized.
• The large attractive forces result in a very
stable structure.
50
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7.1 Ions > Properties of Ionic Compounds
Ionic compounds generally have
high melting points.
51
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7.1 Ions >
CHEMISTRY
& YOU
Would you expect to find sodium
chloride in underground rock deposits
as a solid, liquid, or gas? Explain.
Sodium chloride is found in
underground rock deposits
as a solid. Like most ionic
compounds, sodium
chloride has a high melting
point (about 800°C).
52
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7.1 Ions > Properties of Ionic Compounds
The coordination number of an ion is the
number of ions of opposite charge that
surround the ion in a crystal.
• In NaCl, each ion has a
coordination number of 6.
– The coordination number of
Na+ is 6 because each Na+ ion
is surrounded by six Cl– ions.
– The coordination number of Cl–
is also 6 because each Cl– ion
is surrounded by six Na+ ions.
53
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7.1 Ions > Properties of Ionic Compounds
In CsCl, each ion has a coordination
number of 8.
• Each Cs+ ion is
surrounded by
eight Cl– ions.
• Each Cl– ion is
surrounded by
eight Cs+ ions.
54
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7.1 Ions > Properties of Ionic Compounds
Titanium dioxide (TiO2), or rutile,
forms tetragonal crystals.
• The coordination
number for the cation
(Ti4+) is 6.
– Each Ti4+ ion is surrounded
by six O2– ions.
• The coordination number
of the anion (O2–) is 3.
– Each O2– ion is surrounded
by three Ti4+ ions.
55
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7.1 Ions > Properties of Ionic Compounds
Ionic compounds can conduct an
electric current when melted or
dissolved in water.
56
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7.1 Ions > Properties of Ionic Compounds
When sodium chloride is melted, the orderly
crystal structure breaks down.
Power source
• If a voltage is
applied across
this molten
mass, cations
migrate freely
to one
electrode and
anions migrate
to the other.
Current meter
Flow of
electrons
Inert metal
electrodes
Flow of
electrons
Cl–
Na+
To (+)
electrode
To (–)
electrode
• This movement of electrons allows electric current to
flow between the electrodes through an external wire.
57
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7.1 Ions > Properties of Ionic Compounds
This solar facility uses molten NaCl for its ability
to absorb and hold a large quantity of heat,
which is used to generate electricity.
58
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7.1 Ions > Properties of Ionic Compounds
Ionic compounds also conduct electric
current if they are dissolved in water.
• When dissolved, the ions are free to move
about in the solution.
59
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7.1 Ions >
When can ionic compounds conduct
an electric current?
A. Only when melted
B. When melted or dissolved in water
C. Only when dissolved in water
D. When solid or melted
60
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7.1 Ions >
Key Concepts
Although they are composed of ions, ionic
compounds are electrically neutral.
Most ionic compounds are crystalline
solids at room temperature.
Ionic compounds generally have high
melting points.
Ionic compounds can conduct an electric
current when melted or dissolved in water.
61
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7.1 Ions >
Glossary Terms
• ionic compound: a compound composed of
positive and negative ions
• ionic bond: the electrostatic attraction that
binds oppositely charged ions together
• chemical formula: an expression that
indicates the number and type of atoms
present in the smallest representative unit of a
substance
62
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7.1 Ions >
Glossary Terms
• formula unit: the lowest whole-number ratio
of ions in an ionic compound; in magnesium
chloride, the ratio of magnesium ions to
chloride ions is 1:2 and the formula unit is
MgCl2
• coordination number: the number of ions of
opposite charge that surround each ion in a
crystal
63
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7.1 Ions >
BIG IDEA
Bonding and Interactions
• The electrostatic forces between the
oppositely charged ions hold the cations
and anions together in an ionic
compound.
• Ionic compounds generally have high
melting points and can conduct an
electric current in solution and in the
molten state.
64
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7.1 Ions >
Chapter 7
Ionic and Metallic Bonding
7.1 Ions
7.2 Ionic Bonds and
Ionic Compounds
7.3 Bonding in Metals
65
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7.1 Ions >
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 corrosionresistant material that
melts at very high
temperatures.
66
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7.1 Ions > 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.
67
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7.1 Ions > 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.
68
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7.1 Ions > Metallic Bonds and Metallic Properties
Metallic bonds are the forces of
attraction between the free-floating
valence electrons and the positively
charged metal ions.
• These bonds hold metals together.
69
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7.1 Ions > 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.
70
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7.1 Ions > Metallic Bonds and Metallic Properties
Properties of Metals
Metals are ductile—that is, they can be
drawn into wires.
Force
• Metals are also
malleable, which
means that they can
be hammered or
pressed into
shapes.
Metal
rod
Die
Wire
71
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7.1 Ions > Metallic Bonds and Metallic Properties
Properties of Metals
When a metal is subjected to pressure, the
metal cations easily slide past one another.
Sea of
electrons
Force
Force
Nonmetal
anion
Metal
cation
Metal
cation
Strong
repulsions
Metal
72
• 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.
Ionic crystal
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7.1 Ions >
CHEMISTRY
& YOU
How are metals and ionic compounds
different? How are they similar?
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.
73
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7.1 Ions > 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.
74
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7.1 Ions > 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.
Chromium
75
• The metallic
elements sodium,
potassium, iron,
chromium, and
tungsten crystallize
in a body-centered
cubic pattern.
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7.1 Ions > Metallic Bonds and Metallic Properties
Crystalline Structure of Metals
In a face-centered cubic arrangement, every atom
has twelve neighbors.
Gold
76
• Among the metals
that form a facecentered cubic
structure are copper,
silver, gold,
aluminum, and lead.
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7.1 Ions > Metallic Bonds and Metallic Properties
Crystalline Structure of Metals
In a hexagonal close-packed arrangement, every
atom also has twelve neighbors.
Zinc
• The pattern is different from the
face-centered cubic arrangement.
• Metals that have a
hexagonal closepacked crystal
structure include
magnesium, zinc, and
cadmium.
77
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7.1 Ions >
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
78
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7.1 Ions > Alloys
Alloys
Why are alloys important?
• Alloys are mixtures of two or more elements,
at least one of which is a metal.
– Brass, for example, is an alloy of copper
and zinc.
79
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7.1 Ions > 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.
80
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7.1 Ions > 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.
81
Stainless Steel
80.6% Fe
18.0% Cr
0.4% C
1.0% Ni
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7.1 Ions > 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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7.1 Ions >
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.
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7.1 Ions > 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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7.1 Ions >
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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7.1 Ions >
BIG IDEA
Bonding and Interactions
• 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.
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