Ionic Compounds
7.4 Metallic Bonds and the
Properties of Metals
Metallic Bonds
 Objectives:
 Describe
a metallic bond
 Relate the electron sea model to the
physical properties of metals
 Define alloys and categorize them into two
basic types
Metallic Bonds
 Properties
of materials are based on
bonding, and the bonding in both metals
and ionic compounds is based on the
attraction of particles with unlike
charges.
 Metals are not ionic but share several
properties with ionic compounds.
Metallic Bonds
 As
solids, metal atoms form lattices,
similar to ionic crystal lattices.
 Each metal atom is surrounded by 8-12
other metal atoms.
 Although metal atoms have at least one
valence electron, they do not share
these electrons with neighboring atoms
nor do they lose electrons to form ions.
Metallic Bonds
 Instead,
the outer energy levels of the
metal atoms overlap.
 The electron sea model proposes that
all metal atoms in a metallic solid
contribute their valence electrons to
form a “sea” of electrons.
Metallic Bonds
 The
electrons are not held by any
specific atom and can move easily from
one atom to the next.
 Because they are free to move they are
often referred to as delocalized
electrons, with the rest of the atom
called a metallic cation.
Metallic Bonds
Metallic Bonds
A
metallic bond is
the attraction of a
metallic cation for
delocalized
electrons.
Properties of Metals
In general, metals have
 moderately high melting
points.


Cations and electrons are
mobile; it does not require
extreme amounts of energy to
move them past each other.
Melting points of metals do
vary greatly, however.
 high

boiling points.
Atoms must be separated
from the group of cations and
electrons; requires a lot of
energy.
Properties of Metals
 Malleable,
meaning they can be
hammered into sheets, and ductile,
meaning they can be drawn into wire.
 Mobile
particles can be pushed or pulled
past each other.
 Durable
 Electrons
even though mobile, are strongly
attracted to the metallic cations. They are
not easily removed from one another.
Properties of Metals
 Good
conductors
 Delocalized
electrons in metal are free to
move, keeping metallic bonds intact.
 Delocalized electrons move heat quickly
from one place to another.
 Electrons themselves move as part of an
electric current when an electric potential is
applied to the metal
 Lustrous
 Delocalized
electrons interact with light
Properties of Metals
 The
mobile electrons in transition
metals consist of s and d electrons
 As the number of delocalized
electrons increases, so do the
properties of hardness and strength.
Metallic Bonds
 Strong
metallic bonds
are found in transition
metals like chromium,
iron and nickel.
Metallic Bonds
 Whereas
alkali metals are considered
soft because they have only one
delocalized electron.
Metal Alloys
 An
alloy is a
mixture of elements
that has metallic
properties.
 See Table 13, pg.
228
Metal Alloys
 The
properties of
alloys differ somewhat
from the properties of
the elements they
contain.
 Steel
is iron mixed with
at least one other
element.
 Properties of iron are
present but steel is
much stronger than
iron alone.
Metal Alloys
 Alloys
most commonly form when the
elements involved are either similar in
size or the atoms of one element are
considerably smaller than the atoms of
the other.
 Two basic types of alloys exist.
Metal Alloys
 Substitutional
Alloy: Atoms of
the original
metallic solid are
replaced by other
metal atoms of
similar size.
 Ex. sterling silver –
Cu atoms replace
some Ag atoms.
Metal Alloys
 Brass,
pewter and
10-carat gold are
also examples of
substitutional
alloys.
Metal Alloys
 An
interstitial alloy is formed when small
holes (interstices) in a metallic crystal
are filled with smaller atoms.
 Carbon
steel (see next slide)
Metal Alloys
 Carbon
 holes
steel
in the iron crystal are filled with
carbon atoms
 the alloy formed is harder and stronger, but
less ductile, than pure iron