UNIT 6 - ELECTRICITY
Section 6.1 - Conductivity
METALLIC BONDING
6.1.a Metallic Bonding
6 https://youtu.be/9lDVDf9AKhQ
or search: Metallic Bonding & Properties
Tutorial [Now with Animations!]
Metallic bonding is the ELECTROSTATIC ATTRACTION between
METAL CATIONS (+)
and
MOBILE VALENCE ELECTRONS (–).
Metals have Giant Structures
“Giant Structures” refer to large, non-molecular arrangements of atoms. Examples of a “giant
structures” are an ionic crystal lattices and covalent network solids.
“Giant” implies that the structure is large, but in truth, variable numbers of atoms are involved.
In a metal, atoms are packed closely together in an orderly manner.
Ex.
Elemental Sodium = sodium metal on its own
A sodium atom on its own has a net charge of
zero since the # of protons =the # of electrons.
When a bunch of sodium atoms get together
they form an orderly 3-D CRYSTAL LATTICE.
But sodium’s valence electron DOESN’T
stay attached to it’s “home atom”…
Metallic Bonding
Each metal atom gives up its VALENCE electrons
to form cations (positive ions).
These electrons do NOT belong to any particular
particular metal atom therefore we say they are
delocalized. They don’t have a specific “home”.
These delocalized valence electrons are mobile
which means they move freely in the space
between the metal ions.
UNIT 6 - ELECTRICITY
Section 6.1 - Conductivity
6.1.a Metallic Bonding
Q. Why do the metal ions give up their valence electrons to this “sea” of mobile, delocalized
electrons?
A.
① Metallic atoms have low electronegativities, which means they tend to lose their outer
shell electrons easily.
② Once a metallic atom has lost its outer shell electron, it forms a positively charged ion
called a cation. This produces electron configurations similar to the noble gases and
hence a more stable state.
stable noble gas electron configuration
Ex.
= a sodium cation
NOTE:
= a valence electron
Only a few of the electrostatic interactions are shown in the figure above.
Metallic bonding is the
ELECTROSTATIC ATTRACTION
(
)
between
METAL CATIONS (+)
and
MOBILE, DELOCALIZED VALENCE ELECTRONS (–).
UNIT 6 - ELECTRICITY
Section 6.1 - Conductivity
6.1.a Metallic Bonding
Another image
showing the
“sea” or
“swarm” like
nature of the
valence electrons:
The outer electrons are so weakly bound to the metal atoms that they are
free to roam across the entire metal. Having “lost” their outer electrons,
individual metal atoms are more like positive ions in a swarm of communal
electrons.
Physical Properties - Explanation
① Solid, high density
Metals are packed tightly in layers.
② High melting and
boiling points
Metal ions are held together by their strong electrostatic attraction
to the delocalized electrons between the ions.
i.e. Metals are held together by strong metallic bonds.
③ Malleable and
Ductile
When a force is applied to a metal, the layers of atoms can
slide over each other easily.
UNIT 6 - ELECTRICITY
Section 6.1 - Conductivity
6.1.a Metallic Bonding
③ Malleable and Ductile (continued)
The metal does not break because the “sea” of mobile electrons is free to move within the
structure, so they continue to attract the cations even when deformed.
Malleable
(can be hammered into sheets)
Ductile
(can be drawn into wires)
UNIT 6 - ELECTRICITY
④
Metals are shiny:
Section 6.1 - Conductivity
Property - Lustre
6.1.a Metallic Bonding
UNIT 6 - ELECTRICITY
Section 6.1 - Conductivity
6.1.a Metallic Bonding
⑤ Good conductor of heat
The movement of delocalized electrons
allows heat to be conducted.
When a metal is heated, the electrons
at the heated end move faster, and they
collide with neighbouring electrons
with lots of energy.
This makes the neighbouring electrons
move more quickly as well, and soon all
the electrons in the metal are moving quickly.
⑥ Good electrical conductor
Metals conduct electricity when
solid and when molten (melted).
Current electricity is the movement
of charged particles in a particular
direction.
This is possible in a metal because
the delocalized, mobile electrons
can move.
As one electron moves away from its “home” atom, a second electron moves into the
“hole” left behind by the first electron.
If you put a positive charge at one end, and a negative charge at the other end of a copper wire,
the electrons will flow in one direction… away from the negative (– charge repels e–‘s)
and towards the positive (+ charge attracts e–‘s)
Now watch the following video that shown an animation of how the delocalized electrons allow a
current to flow in a wire.
6
What is a copper atom?
Engineering Technology
Simulation Learning Videos
(1:44)
https://youtu.be/O4lkxkbeo3s
UNIT 6 - ELECTRICITY
Section 6.1 - Conductivity
6.1.a Metallic Bonding
Exercises:
1.
Metals have delocalized valence electrons.
a)
What does it mean that the valence electrons are delocalized?
b)
In addition to being delocalized, the valence electrons of metals are also mobile.
What does it mean that these electrons are mobile?
2.
The valence electrons are said to form a “_________” (or “_______________”) of mobile delocalized
electrons.
fill in the blanks
3.
a)
Fill in the blanks
stable ____________________ _________ electron configuration
= a sodium _____________
= a _____________ electron
b)
Draw in between 5 and 10 electrostatic attractions using dashed lines. --------
c)
These electrostatic attractions occur between stationary ________________________ and
the mobile ______________________ ____________________________.
d)
What type of bond is formed by these electrostatic attractions?
UNIT 6 - ELECTRICITY
4.
Section 6.1 - Conductivity
6.1.a Metallic Bonding
Use metallic bonding and the “sea of mobile electrons” model to explain why metals are
a)
good conductors of heat.
b)
good conductors of electricity.
c) malleable and ductile
d) lustrous
5.
Compare and contrast the forces involved in ionic bonding, covalent bonding and metallic
bonding. (When you are asked to “compare and contrast”, that means you should list the things
that are similar or the same and the things that are different.
UNIT 6 - ELECTRICITY
Section 6.1 - Conductivity
6.1.a Metallic Bonding
6.1.a KEY
ANSWERS:
1.
Metals have delocalized valence electrons.
a)
What does it mean that the valence electrons are delocalized?
The electrons are not bound to a “home atom” or bond.
b)
In addition to being delocalized, the valence electrons of metals are also mobile.
What does it mean that these electrons are mobile?
These delocalized electrons are “mobile”…free to move from one atom to another.
2.
sea
swarm
The valence electrons are said to form a “_________”
(or “_______________”)
of mobile delocalized
electrons.
fill in the blanks
3.
a)
Fill in the blanks
stable ____________________
_________
noble
gas electron configuration
ion
= a sodium _____________
valence
= a _____________
electron
FOR EXAMPLE:
b)
Draw in between 5 or more electrostatic attractions using dashed lines. --------
c)
cations
These electrostatic attractions occur between stationary ________________________
and
valence
electrons
the mobile ______________________
____________________________.
d)
What type of bond is formed by these electrostatic attractions?
a metallic bond
UNIT 6 - ELECTRICITY
Section 6.1 - Conductivity
6.1.a Metallic Bonding
6.1.a KEY
4.
Use metallic bonding and the “sea of mobile electrons” model to explain why metals are
a)
When a metal is heated, the electrons at the heated
end move faster, and they collide with neighbouring electrons with lots of
energy. This makes the neighbouring electrons move more quickly as well, and
soon all the electrons in the metal are moving quickly.
b)
The “sea” delocalized mobile electrons can move.
As one electron moves away from its “home” atom, a second electron moves
into the “hole” left behind by the first electron. If you put a positive charge at
one end, and a negative charge at the other end of a copper wire, the electrons
will flow in one direction… away from the negative (– charge repels e–‘s)
and towards the positive (+ charge attracts e–‘s)
good conductors of heat.
good conductors of electricity.
c) malleable and ductile
The metal does not break because the “sea” of mobile electrons is free to move within
the structure, so the mobile electrons continue to attract the cations even when the
overall structure is deformed.
d) lustrous Light rays bounce off the delocalized electrons.
5.
Compare and contrast the forces involved in ionic bonding, covalent bonding and metallic
bonding. (When you are asked to “compare and contrast”, that means you should list the things
that are similar or the same and the things that are different.
•
All 3 types of bonding involve ELECTROSTATIC ATTRACTIONS between positive and
negative charges.
•
In a covalent bond
- the “positive things” are the nuclei of the bonded atoms
- the “negative things” are the shared electrons in the bond
•
In an ionic bond
- the “positive things” are cations
- the “negative things” are anions
•
In a metallic bond
- the “positive things” are the metal cations
- the “negative things” are the delocalized valence electrons