8/6/2019 Notes for Metallic Bonding
1/12
Anglo-Chinese School (Independent)
The Physical Setting Structure of Matter: What Lies Beneath
Objectives:
Section A: Review of Metallic Bonding
Section B: Physical Properties of Metals
Section C: Overall Review of Chemical Bonding
Section A Review of Metallic Bonding
Figure 1: Diagram of a metallic lattice.
Atoms in metals are packed very closely in an orderly arrangement.
Each atom loses its valence electrons to become a positive ion.
Metals are described as having a regular arrangement of positive ions in a sea of
delocalized electrons. The electrons are free to move about within the structure
and are said to form a sea of electrons around the metal ions.
There are strong forces between the positive ions and electrons metallic bonding
Zoom In
8/6/2019 Notes for Metallic Bonding
2/12
Section B: Physical Properties of Metals
Property 1: High Melting Point and Boiling Point
What do you understand by the term melting point?
- Melting Process:
When a pure solid is heated, the particles in it gain energy and the
vibration of the particles increases until eventually the particles are able to
overcome the forces that hold them in their fixed positions.
- Hence, the melting point is the fixed temperature at which a pure solid
turns into a liquid at atmospheric pressure.
What do you understand by the term boiling point?
- Boiling process:
When a pure liquid is heated, the particles in it gains energy and move
more quickly. Eventually, the particles have enough energy to completely
break the forces holding them together. The particles are now able to
move freely and far apart.
- Hence, the boiling point is the temperature at which a pure liquid turnsinto a gas at atmospheric pressure.
8/6/2019 Notes for Metallic Bonding
3/12
Why do metals generally have a high melting point and high boiling point?
Reason:
As the forces of attraction between the sea of delocalized electrons and positive
ions (cations) is very strong, a large amount of heat is required to break up the
giant lattice. Hence, metals have a high melting point and boiling point.
List some metals that have a high melting and boiling point.
Magnesium, Iron, Copper and Tungsten
List some metals that have a low melting and boiling point.
Mercury and the Group I elements
Application/Uses:
- Tungsten is used to make the filaments of light bulbs
due to its high melting point. It does not melt even
when glowing white-hot inside a bulb.
- Welding is the most economical and efficient way
to join metals permanently. It is the only way of
joining two or more pieces of metals to make them
act as a single piece.
8/6/2019 Notes for Metallic Bonding
4/12
Property 2: High Density
Why do metals generally have a high density?
Reason:
As the ions in metals are closely packed in the lattice, they generally have high
densities.
Property 3: Malleable and Ductile
What do you understand by the term malleable?
A substance is said to be malleable when it can be beaten into sheets.
What do you understand by the term ductile?
A substance is said to be ductile when it can be pulled out into wires.
Figure 2: Sliding of one layer of metal ions over others when a force is applied.
If a small stress is put onto the metal, the layers of atoms will start to roll
over each other. If the stress is released again, they will fall back to their original
positions. Under these circumstances, the metal is said to be elastic.
free electron
+
+
+ +
+
+
+
+
++
+
+
++
+
+
+
+
+ +
metal ion
slip plane
+
+
+ +
+
+
+
+
++
+
+
+
+
+
+
+
+ +
applied force
(a) Before a force is applied, the metal
atoms form an orderly and rigidarrangement.
(b) When a force is applied, one layer of
metal ions slides over the other.
8/6/2019 Notes for Metallic Bonding
5/12
Figure 3: Sliding of one layer of metal ions over others when a small stress is
applied.
Figure 4: Sliding of one layer of metal ions over others when a large stress is
applied.
Why are pure metals generally malleable and ductile?
Reason:
Though the attraction between the sea of electrons and the metal ions is strong, it
is not rigid. Combined with the regular arrangement of the ions in layers, the
layers of ions can slip over each other into new positions when a force is applied
to the metal, without breaking the metallic bond. Hence, metals are malleable and
ductile.
List some examples of metals that are malleable and ductile.
Aluminum
Application/Uses:
- Aluminum is used to make foil for wrapping purposes due to its high
malleability.
Property 4: Thermal Conductivity
8/6/2019 Notes for Metallic Bonding
6/12
Why are metals usually good conductors of heat?
When one end of a piece of metal is heated, the positive ions vibrate more
vigorously. The vibrating ions transfer energy to the mobile electrons. These
mobile electrons move to other parts of the metal and transmit this energy to other
positive ions. In this way, heat is transferred quickly throughout the metal.
List some examples of metals that are good conductors of heat.
Copper and aluminum
Application/Uses:
- Copper is used to make kitchen utensils such as
kettles, steam pipes, boilers, etc., due to its heat
conductivity.
- Aluminum is used to make kitchen utensils such
as kettles, pots and pans due to its heat
conductivity.
8/6/2019 Notes for Metallic Bonding
7/12
Property 5: Electrical Conductivity
Why are metals good conductors of electricity?
Figure 5: Mobile electrons in a metal connected to an electrical circuit.
List some examples of metals that are good conductors of electricity.
Copper and aluminum
Application/Uses:
- Large amounts of copper are used to make electrical wires and
cables due to its good electrical conductivity.
- Aluminum or its alloys are widely used in making overhead lines
and energy cables due to its good electrical conductivity.
Ammeter
Metal
+ -
e-
e-
e-
e-
e-
e-
e-e-
e-
e-
e-
More electrons enter
the metal from the
negative terminal
The positive ions remain in
position while the transferof electrons takes place.
Free electrons leave
the metal and moves
towards the positiveterminal
8/6/2019 Notes for Metallic Bonding
8/12
8/6/2019 Notes for Metallic Bonding
9/12
Characteristic Ionic Compound Covalent Compounds Metal
Simple Molecule Macromolecule
Bonding
between:
Metal and non-metal Non metals only Non-metals only Metals only
Particles
present:
Ions
(Cations & Anions)
Molecules Atoms Fixed positive ions in a
sea of delocalized
electrons
State at r.t.p: Solid Gas or volatile liquid Solid Solid
Melting point
& Boiling
point:
High Low High High
*Exception: Hg
Strong electrostatic forces
of attraction between
oppositely charged ions. A
lot of energy is required to
break them.
Weak Van der Waals
forces between molecules.
Little energy is required to
break them.
Exist as macromolecule
with strong covalent bonds
between atoms. A lot of
energy is required to break
them.
Strong metallic bond
between ions and
delocalized electrons.
Electrical
Conductivity:
Conducts electricity only
in molten and aqueous
state but not in solid state.
Does not conduct
electricity in any state.
Does not conduct
electricity in any state.
*Exception: Graphite is a
conductor in solid state.
Conducts electricity in
solid and molten state.
In molten and aqueous
state, ions are mobile and
able to conduct electrical
Exist as molecules.
Absence of mobile charged
particles.
Absence of mobile charged
particles in diamond,
silicon and silica.
Presence of mobile
electron cloud which are
able to carry electrical
8/6/2019 Notes for Metallic Bonding
10/12
charges.
In solid state, ions are held
rigidly in fixed positions
and are unable to move
thus unable to conduct
electricity.
Graphite can conduct
electricity due to the
presence of mobile
electrons which can carry
electrical charges.
charges.
Solubility: Soluble in polar solvents
like water.
Soluble in non-polar /
organic solvents like
chloroform and benzene.
Insoluble in water.
Insoluble in water and
almost all solvents.
Insoluble in water.
Examples: Sodium Chloride Iodine Diamond Graphite Magnesium
Diagram:
8/6/2019 Notes for Metallic Bonding
11/12
define asdefine as
forms
from
forms
from
BONDING
Covalent
Sharing of electron (s)
non-metals and non-metals
macromolecules simple molecules
diamond, graphite, siliconand silicon dioxide
elements compounds
H2, O
2, N
2, Cl
2HCl, H
2O, NH
3
can have
single bonds
H-H
double bonds
O=O
triple bonds
NN
AlCl3
operties
(1) High m.p. and b.p.(2) Conducts electricity in
molten or aqueous state
(3) Dissolves in polar solvents(4) Usu. solid at r.t.p.
define a
NaCl
1e-
Transfer of electron (s)
metals to non-metals
Properties
(1) High m.p. and b.p.(2) Non-conductors of
electricity*exception: graphite
(3) Insoluble in allsolvents
(4) Exist as a solid at
r.t.p.
Ionic (Electrovalent) Metallic
Lattice of positive fixeions in a sea of electron
from
metals only
forms
Properties
(1) High m.p. and
(2) High density(3) Malleable and
ductile(4) Conductors of
heat(5) Conductors of
electricity
(6) Solids at r.t.p.
ions
Properties(1) Low m.p. and b.p.
(2) Non-conductors of electricity(3) Dissolves in non-polar solvents
(4) Usu. exists as liquids and gases at r.t.p.
NaCl
2e- 3e-
MgCl2 AlCl3
lattice structure
8/6/2019 Notes for Metallic Bonding
12/12
Section C Overall Review of Chemical Bonding
Substance Formula Bonding diagram Structure
type
sodiumchloride
NaCl ionic
methane CH4 simple
molecular
carbon
dioxide
CO2 simple
molecular
diamond C giant
molecular
copper Cu metallic
Top Related