Notes for Metallic Bonding

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


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.


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.


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.


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


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.


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


8/12


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


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:


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


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

Notes for Metallic Bonding

Documents