Chapter 7/Lesson 3
Metallic Bonds
P:
Objectives
Describe the structure of a metal crystal.
Identify properties of metals.
Introduction
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WHAT ARE METALS:
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Metallic Bonding Video
Metals
Metals are made up of closely
packed cations surrounded by
electrons, rather than neutral atoms
or ions
Outer electron clouds of the metal
ions overlap
What are
Metals?
On the periodic table, a
diagonal or stair step line
drawn from boron (B) to
polonium (Po) separates
the metals from the
nonmetals. Elements on
this line are metalloids,
sometimes called semimetals; elements to the
lower left are metals;
elements to the upper
right are nonmetals.
Almost 80% of the
elements on the periodic
table are metals.
Metallic Bond
Model
Electron sea model – metals in a solid
contribute their valence electrons to form a
“sea of electrons”
◦ Valence electrons are not held by any specific
atom and can move easily from one atom to
the next
Delocalized electrons –are free to move in
the “sea of electrons”
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Metallic Bonds
The valence electrons of metal atoms can drift freely from one part of the metal
to another- this is sometimes
called a “sea of electrons”
Metallic bonds consist of
the attraction between these
free floating electrons and the
positively charged metal ions (cations). This attraction is the “bond” that holds
metals together.
Metallic Bond
Definition: The attraction of the delocalized electrons for the positively
charged metal ions
Metal bonded to metal
Each ion is bonded to all neighboring cations by the “sea” of valence electrons
Properties of
Metals
In general, metals have moderately high
melting and boiling points
Good conductors of heat and electricity
Malleable and Ductile
◦ Mobile electrons can easily be pushed or
pulled past each other
Physical Properties
of Metals
Lusterous- they are shiny!
High density- atoms are tightly packed.
Good conductors of electricity and heat.
◦ Reason- electrons can flow freely.
Physical
Properties of
Metals
Ductile- they can be
drawn into wires AND
Malleable- they can be
hammered into shapes
◦ Reason- cations can slide
easily past each other
because the sea of
electrons insulates them
and prevents strong
repulsions.
…on the
other
hand
IONIC COMPOUNDS
ARE BRIT TLE AND
BREAK EASILY? WHY
Game
Time
Properties of metals
Matching
Properties Hit the correct
mole game
Physical Properties of Metals
Metal ions are arranged in very compact orderly patterns.
–Similar to the way apples are stacked at the grocery store.
Pure metals form the simplest kinds of crystals
Structure of
Metals
Metal atoms are arranged in very
compact and orderly patterns
Metals that contain just one kind
of atom are among the simplest
forms of all crystalline solids
Game Time
Metallic Bonds Game
Chemical Properties of Metals
Most metals are chemically
unstable and will react will
oxygen in the air- that is they
form oxides- over varying
timescales (for example iron
rusts over years
and potassium
burns in seconds).
Chemical Properties
of Metals
-The alkali metals react quickest followed by the
alkaline earth metals.
-The transition metals take much longer to
oxidize (such as iron, copper, zinc, nickel).
Others, like palladium, platinum and gold, do
not react with the atmosphere at all.
-Some metals form a barrier layer of oxide on
their surface which cannot be penetrated by
further oxygen molecules and thus retain their
shiny appearance and good conductivity for
many decades (like aluminium, some steels,
and titanium).
Alloys
Very few metals that you encounter
daily are pure metals. Most metals are
alloys, a mixture of two or more
elements of which at least one is a
metal.
Alloys are important because their
properties are often superior to those
of their component elements.
• Examples:
• Brass is an alloy of copper and zinc
• Sterling silver is an alloy of silver
(92%) and copper (8%)
• Stainless Steel is an alloy of iron
(81%), chromium (18%), nickel (1%),
and trace amounts of carbon.
• Examples:
• Sterling silver is harder and more
durable than pure silver, but still
soft enough to make jewelry and
tableware.
• Brass is harder and easier to shape
than either copper or zinc
Alloy is a mixture of two or more elements (at least
one must be a metal)
Metal
Alloys
Alloy has metallic properties often superior to those of
their component elements
-Bronze: copper + tin
-Steel: iron + carbon + other metals
-Sterling silver: silver + copper
Zn
Brass though
a magnifier
Brass at the
atomic level
Cu
2 common types
of Alloys
Substitutional:
one metal about the size of the other replaces
it
examples: Brass, pewter, 10-carat gold
Interstitial:
one metal smaller than the other fits between
it
example: Carbon steel
Types of Alloys
SUBSTITUTIONAL
Atoms have relatively the same
size
INTERSTITIAL
Atoms of different sizes