Chapter 9
Structures and properties of substances
9.1 Structures of substances
9.2 Simple molecular structures
9.3 Giant covalent structures
9.4 Giant ionic structures
9.5 Giant metallic structures
9.6 Comparison of structures and properties of
substances
P. 1 / 73
9.7 Predicting structures from physical properties
9.8 Predicting physical properties from bonding
and structure
9.9 Applications of substances according to their
properties
Key terms
Progress check
Summary
Concept map
P. 2 / 73
9.1 Structures of substances
Classification of substances according to structure
The structure of a substance is a description of:
what its constituent particles are, and
how they are arranged and packed together.
Under room conditions, all substances exist as
either:
molecular structures or
giant structures
P. 3 / 73
Molecular structures
Molecular structures consist of discrete molecules.
The atoms within a molecule are bonded together
by strong covalent bonds.
Each molecule is attracted to neighbouring
molecules by intermolecular forces only.
9.1 Structures of substances
P. 4 / 73
Two types of molecular structures:
Simple molecular structures
Examples: iodine (solid), bromine (liquid)
and chlorine (gas)
Macromolecules
usually solids under room conditions
Examples: plastics, proteins and some
carbohydrates like starch
9.1 Structures of substances
P. 5 / 73
(a)
(b)
Figure 9.1 (a) Starch, which can be found in bread, and (b) polyethene,
which can be used to make plastic bag, are made up of macromolecules.
9.1 Structures of substances
P. 6 / 73
Giant structures
All particles (trillions of atoms or ions) are held
together by strong chemical bonds.
A continuous giant lattice forms, in which:
the particles are packed in a regular pattern
no discrete molecules exist
Almost all substances with giant structures are
solids under room conditions.
Learning tip
For polyethene, the formula is represented by
–(CH2CH2)n–, where n is a whole number from
100 to 30 000.
9.1 Structures of substances
P. 7 / 73
Molecular
structures
Substances
Simple molecular
structures
Macromolecules
Giant covalent
structures
Giant
structures
Giant ionic
structures
Giant metallic
structures
Figure 9.2 Classification of substances according to structure.
9.1 Structures of substances
P. 8 / 73
EXAMPLES
Elements
Non-metals
Simple
molecular
structures
hydrogen (H2),
iodine (I2)
Metals
Covalent
Ionic
water (H2O),
carbon
dioxide (CO2)
polyethene
–(CH2CH2)n–
Macromolecules
Giant covalent
structures
Compounds
diamond, graphite
(different forms of
carbon)
silicon dioxide
(SiO2)
sodium
chloride
(NaCl)
Giant ionic
structures
Giant metallic
structures
copper (Cu),
iron (Fe)
Figure 9.2 Classification of substances according to structure.
9.1 Structures of substances
P. 9 / 73
Key point
All substances exist as either
molecular structures or _______________
giant structures
___________________
under room conditions.
9.1 Structures of substances
P. 10 / 73
9.2 Simple molecular structures
Most non-metal elements and covalent compounds
are composed of simple, discrete molecules.
Examples: hydrogen, iodine, water, carbon dioxide
Structure of carbon dioxide
Each carbon dioxide molecule consists of one
carbon atom and two oxygen atoms covalently
bonded together.
Under room conditions, carbon dioxide is a gas.
Under temperatures below –78.5°C, carbon dioxide
gas changes to a solid (dry ice) directly without
going through the liquid state.
P. 11 / 73
Carbon dioxide molecules are held together by
weak intermolecular forces (called van der
Waals’ forces) and packed closely together in
a regular pattern.
But they are still discrete molecules.
Learning tip
Van der Waals’ forces are much weaker than ionic
bond, covalent bond and metallic bond. In general,
the larger the molecular size, the greater will be the
van der Waals’ forces between molecules.
9.2 Simple molecular structures
P. 12 / 73
a carbon dioxide
molecule
Figure 9.3 In the structure of dry ice, CO2 molecules are held together by
weak van der Waals’ forces. Within each CO2 molecule, the atoms are
held together by strong covalent bonds.
9.2 Simple molecular structures
P. 13 / 73
Structure of iodine
In an iodine crystal,
iodine molecules are also held together by
weak van der Waals’ forces
iodine molecules packed closely together in
a regular pattern
an iodine molecule
Figure 9.4 In the crystal structure of iodine, I2 molecules are held together
by weak van der Waals’ forces in a regular pattern. Repetition of this
pattern trillions of times would result in a crystal.
9.2 Simple molecular structures
P. 14 / 73
Properties of substances with a simple molecular
structure
1. They have low melting points and boiling
points.
Under room conditions, substances with a simple
molecular structure are
gases,
volatile liquids, or
solids with low melting points
9.2 Simple molecular structures
P. 15 / 73
Molecules are held together only by weak
intermolecular forces, little heat energy is needed
to separate the molecules.
Figure 9.5 Substances with a simple molecular structure may be gases,
liquids or solids.
9.2 Simple molecular structures
P. 16 / 73
Learning tip
A volatile liquid evaporates quickly under room
conditions.
2. Solids with a simple molecular structure are
soft.
Intermolecular forces are weak.
It is easy to separate the molecules and break
down the crystal structure.
9.2 Simple molecular structures
P. 17 / 73
3. Solids with a simple molecular structure are
usually slightly soluble or insoluble in water,
but soluble in non-aqueous solvents.
Example: Iodine
Only slightly soluble in water
Very soluble in non-aqueous solvents
9.2 Simple molecular structures
P. 18 / 73
The attractive forces between water molecules
are quite strong.
The weak attractive forces are not strong enough
to overcome the attractive forces between water
molecules. Thus, iodine does not dissolve readily
in water.
In non-aqueous solvents, the molecules are held
together by weak attractive forces. Thus, iodine
molecules can mix together with the molecules of
non-aqueous solvent readily.
9.2 Simple molecular structures
P. 19 / 73
weak forces between
iodine and water
molecules
iodine molecules
water molecules
Figure 9.6 Iodine is only slightly soluble in water.
9.2 Simple molecular structures
P. 20 / 73
stronger
attractive forces
between water
molecules
attractive forces between iodine
molecules and molecules of non-aqueous
solvent are similar to those between
molecules of non-aqueous solvent
molecule of non-aqueous
solvent
iodine
molecule
Figure 9.7 Iodine dissolves readily in non-aqueous solvent.
9.2 Simple molecular structures
P. 21 / 73
4. They are usually non-conductors of electricity
They do not contain mobile ions or delocalized
electrons to conduct electricity.
However, aqueous solutions of a few molecular
substances conduct electricity. This is because
mobile ions form when they dissolve in water.
Examples: hydrogen chloride and ammonia
Class practice 9.1
9.2 Simple molecular structures
P. 22 / 73
9.3 Giant covalent structures
Giant covalent structures
atoms are joined by strong covalent bonds to
form a giant network
Covalent bonds extend throughout the whole
structure. There are no discrete molecules.
Examples: diamond, graphite and quartz
P. 23 / 73
Structure and properties of diamond
Diamond is one form of carbon.
Each carbon atom is covalently bonded to four
other carbon atoms, forming a three-dimensional
giant network.
carbon
atoms
Covalent
bonds
Figure 9.8 The three-dimensional structure of diamond.
9.3 Giant covalent structures
P. 24 / 73
To break the structure, a large number of strong
covalent bonds between carbon atoms must be
broken.
This explains extreme hardness and very high
melting point (3550°C) of diamond.
Diamond cannot conduct electricity because it
does not contain delocalized electrons.
Skill corner 9.1
9.3 Giant covalent structures
P. 25 / 73
Structure and properties of graphite
Graphite is another form of carbon.
It also has giant covalent structure.
Carbon atoms are arranged in flat, parallel layers.
Each layer contains many six-membered carbon
rings.
strong covalent bonds (within layers)
weak van der
Waals’ forces
(between layers)
Figure 9.9 The layered structure
of graphite.
9.3 Giant covalent structures
P. 26 / 73
Each carbon atom is covalently bonded to only
three other carbon atoms in its layer.
One outer electron of each carbon atom is
delocalized.
They are free to move from one six-membered
carbon ring to the next within a layer.
Thus, graphite can conduct electricity.
Learning tip
Graphite is the only non-metal that conducts
electricity.
9.3 Giant covalent structures
P. 27 / 73
Graphite is soft, easy to cleave and has
lubricating property.
Only weak van der Waals’ forces exist between
the adjacent layers.
The layers are able to slide over each other.
Graphite has a very high melting point (3730°C).
It requires the breaking of strong covalent bonds
between carbon atoms within the layers.
9.3 Giant covalent structures
P. 28 / 73
Property
Appearance
Hardness
Melting point (°°C)
Electrical
conductivity
Diamond
Graphite
colourless solid
black solid
very hard
soft, brittle
3550
3730
non-conductor
conductor
Table 9.1 Some properties of diamond and graphite.
Think about
9.3 Giant covalent structures
P. 29 / 73
Structure and properties of quartz
Quartz is a crystalline form of silicon dioxide (or
silicon(IV) oxide).
Silicon dioxide (SiO2) is a compound with a giant
covalent structure.
Silicon and oxygen atoms are held together by
covalent bonds throughout the whole structure.
Each silicon atom is bonded to four oxygen atoms.
Each oxygen atom is bonded to two silicon atoms.
9.3 Giant covalent structures
P. 30 / 73
It has a very high melting point (1610°C).
It does not conduct electricity no matter it is
in the solid or molten state.
silicon atom
oxygen atom
silicon and oxygen
atoms are held
together by
covalent bonds
throughout the
whole structure
Figure 9.10 The giant covalent structure of silicon dioxide. Note that this
represents only a very small part of the giant lattice, which extends in all
directions.
9.3 Giant covalent structures
P. 31 / 73
Properties of substances with a giant covalent
structure
1. They are all solids with very high melting points.
In melting the solid, a lot of heat energy must be
supplied to break a large number of strong
covalent bonds in the structure.
9.3 Giant covalent structures
P. 32 / 73
strong covalent
bonds
strong
covalent
bonds
melting (a lot of
energy is needed)
giant covalent structure
Figure 9.11 To melt a substance with a giant covalent structure, a large
number of strong covalent bonds must be broken.
9.3 Giant covalent structures
P. 33 / 73
2. All (except graphite) are hard.
They have a network of strong covalent bonds
in their structures.
The atoms cannot slide over one another.
3. They are insoluble in any solvent.
They are insoluble in water and non-aqueous
solvents.
The atoms are held together by strong
covalent bonds. It is difficult to separate
them.
9.3 Giant covalent structures
P. 34 / 73
4. All (except graphite) are non-conductors of
electricity.
All the outermost shell electrons of the atoms
in substances with a giant covalent structure
are held firmly in covalent bonds.
There are no delocalized electrons in the
structure.
Experiment 9.1
Class practice 9.2
9.3 Giant covalent structures
P. 35 / 73
9.4 Giant ionic structures
An ionic compound usually forms when a metal
combines with a non-metal.
It consists of positive and negative ions held
together by ionic bonds.
The ions are regularly packed to form a
continuous, three-dimensional giant ionic
structure.
P. 36 / 73
Structure of sodium chloride
Example: sodium chloride
Positively charged ions (Na+) and negatively
charged ions (Cl–) are held together by ionic bonds.
They are packed regularly so that each ion is
surrounded by six ions of the opposite charge.
+
–
+
–
+ –
+
–
+
–
+
+ –
–
–
Na+ ion
Cl– ion
+
+
–
Cl– ion
Figure 9.12 Sodium chloride has a giant ionic structure. It consists of
Na+ and Cl– ions held together by ionic bonds.
9.4 Giant ionic structures
P. 37 / 73
Na+ ion
Learning tip
Figure 9.12 shows just a few Na+ and Cl– ions. Even
a single sodium chloride crystal contains trillions of
ions.
The ions are arranged to form a cubic structure.
The giant structure contains equal numbers of
Na+ and Cl– ions.
9.4 Giant ionic structures
P. 38 / 73
Structure of caesium chloride
Each caesium ion (Cs+) is surrounded by eight
chloride ions (Cl–).
Each chloride ion is in turn surrounded by eight
caesium ions.
or
Cs+ ion
Cl– ion
Figure 9.13 Caesium chloride has a giant ionic structure. It consists of
Cs+ and Cl– ions held together by ionic bonds.
9.4 Giant ionic structures
P. 39 / 73
Properties of ionic compounds
1. They are crystalline in the solid state.
Figure 9.14 A large crystal of copper(II) sulphate.
9.4 Giant ionic structures
P. 40 / 73
2. They are hard but brittle.
The oppositely charged ions are held together
by strong ionic bonds which makes the
compounds hard.
When under stress, the relative movement of
the ions brings ions of the same charge close to
each other. This results in repulsion. Therefore,
they are brittle.
9.4 Giant ionic structures
P. 41 / 73
3. They usually have high melting points and
boiling points.
Example: sodium chloride
Melting point: 808°C
Boiling point: 1465°C
A lot of heat energy is required to overcome the
strong ionic bonds between the ions during
melting and boiling.
9.4 Giant ionic structures
P. 42 / 73
4. Most of them are soluble in water, but insoluble
in non-aqueous solvents.
Example: sodium chloride
It is soluble in water.
When a sodium chloride crystal is added to water,
attraction exists between ions in sodium chloride
and water molecules.
This attraction causes the ions to move away from
the crystal and go into the water.
9.4 Giant ionic structures
P. 43 / 73
Then water molecules surround the ions.
The ions are said to be hydrated.
Cl– ion
water molecules
Na+ ion
hydrated sodium ion
hydrated chloride ion
Figure 9.15 Sodium chloride dissolves in water, forming hydrated ions.
9.4 Giant ionic structures
P. 44 / 73
No such strong attraction exists between the ions
in sodium chloride and molecules of non-aqueous
solvents like tetrachloromethane.
Thus, sodium chloride is insoluble in non-aqueous
solvents.
Learning tip
Attraction exists between ions and water molecules.
This is because one end of a water molecule has a
slightly positive charge while another end has a
slightly negative charge.
9.4 Giant ionic structures
P. 45 / 73
5. They conduct electricity when molten or in
aqueous solution.
When molten or in aqueous solution, the ions
become mobile and can conduct electricity.
Therefore, they are electrolytes.
Example 9.1
Class practice 9.3
Experiment 9.2
9.4 Giant ionic structures
P. 46 / 73
9.5 Giant metallic structures
Structure of metals
Metallic bond forms between delocalized
electrons and the metal ions in a metal.
Metal ions are packed closely together in a
regular pattern in the metal.
Giant metallic structure
A giant lattice of metal ions surrounded by a
‘sea’ of delocalized electrons.
P. 47 / 73
positively charged metal ions
a ‘sea’ of delocalized electrons
Figure 9.16 In a giant metallic structure, positively charged metal ions are
surrounded by a ‘sea’ of delocalized electrons.
9.5 Giant metallic structures
P. 48 / 73
Properties of metals
1. Metals are good conductors of electricity.
2. Metals are good conductors of heat.
heat transfer by collisions of electrons
+
+
+
+
+
heat source
+
+
+
+
+
+
+
metal piece
Figure 9.17 Metal conducts heat by collision of electrons.
Animation (How metals conduct electricity and heat)
9.5 Giant metallic structures
P. 49 / 73
3. Most metals are solids with high melting points.
A lot of heat energy is required to break the
strong metallic bonds in a giant metallic
structure.
4. Most metals have high densities.
5. Metals are malleable (can be rolled into sheets
and other shapes) and ductile (can be drawn
into wires).
When we apply force to a piece of metal, the
layers of ions can slide over one another.
This is because the non-directional metallic
bonds continue to hold the metal ions together.
9.5 Giant metallic structures
P. 50 / 73
great force
layers of
metal ions
slide over
one another
metal
ions
metal ions settle into new positions
under pressure
Figure 9.18 Metals can be re-shaped without breaking.
Class practice 9.4
9.5 Giant metallic structures
P. 51 / 73
9.6 Comparison of structures and properties
of substances
Simple
molecular
structure
H2, I2, H2O,
(1) Examples
NH3, CCl4
(2) Structure
Giant
covalent
structure
C (diamond),
C (graphite),
SiO2
giant lattice
small discrete of atoms
molecules e.g. e.g. C
H2
(diamond)
Giant ionic
structure
NaCl, CaO,
KOH
giant lattice
of ions
e.g. NaCl
Giant
metallic
structure
All metals
giant lattice
of metal ions
surrounded
by a ‘sea’ of
delocalized
electrons
Table 9.2 Comparison of structures and properties of different kinds of
substances.
P. 52 / 73
Simple molecular
structure
strong covalent
bonds bind atoms
together within a
(3) Bonds
molecule; separate
holding
molecules are
constituent
attracted by weak
particles
intermolecular
forces (e.g. van der
Waals’ forces)
Giant
covalent
structure
Giant ionic
structure
Giant
metallic
structure
metallic
bonds link
covalent
ionic bonds the metal
bonds link
link
ions
atoms
oppositely
(positively
throughout charged ions charged)
the network throughout and the ‘sea’
structure
the structure of electrons
(negatively
charged)
Table 9.2 Comparison of structures and properties of different kinds of
substances.
9.6 Comparison of structures and properties of substances
P. 53 / 73
Simple
molecular
structure
(4) Physical
gases, volatile
properties
liquids or solids of
(a) State under
low melting points
room conditions
Giant
covalent
structure
Giant
ionic
structure
Giant
metallic
structure
solids
solids
solids
(except
mercury)
(b) Melting point
low
very high
high
usually high
(c) Hardness of
solid form
soft
usually
hard
hard
usually hard
Table 9.2 Comparison of structures and properties of different kinds of
substances.
9.6 Comparison of structures and properties of substances
P. 54 / 73
Simple
molecular
structure
(d) Solubility in
(i) water
(ii) nonaqueous
solvents
Giant
covalent
structure
Giant ionic
structure
Giant
metallic
structure
(i) insoluble
(except
(i) most are
(i) most are
where
insoluble (i) insoluble
soluble
there is
(ii) generally (ii) insoluble
(ii) insoluble
reaction
soluble
with water)
(ii) insoluble
Table 9.2 Comparison of structures and properties of different kinds of
substances.
9.6 Comparison of structures and properties of substances
P. 55 / 73
Simple
molecular
structure
non-conductors
Note: A few (e.g.
hydrogen
(e) Electrical chloride) react
conductivity with water to
form a solution
which conducts
electricity
Giant
covalent
structure
Giant ionic
structure
Giant
metallic
structure
non-conductors
when solid;
nongood
conductors
good
conductors
(except
conductors
when molten or
graphite)
in aqueous
solution
Table 9.2 Comparison of structures and properties of different kinds of
substances.
9.6 Comparison of structures and properties of substances
P. 56 / 73
9.7 Predicting structures from physical
properties
Physical properties
Yes
1. Is the substance a gas or
liquid under room conditions?
No
2. Does the substance have a
low melting point?
Yes
No
3. Does the substance conduct
electricity in the solid state?
Yes
Structure
Simple
molecular
structure
Giant
metallic
structure
No
Figure 9.19 Predicting the structure of a substance from its physical
properties.
P. 57 / 73
Physical properties
3. Does the substance conduct
electricity in the solid state?
Yes
No
4. Does the substance conduct
electricity when molten or in
aqueous solution?
Yes
Structure
Giant
metallic
structure
Giant
ionic
structure
No
5. Does the substance have a
very high melting point?
Yes
Giant
covalent
structure
Figure 9.19 Predicting the structure of a substance from its physical
properties.
9.7 Predicting structures from physical properties
P. 58 / 73
Learning tip
If the answer to question 3 is ‘yes’, the substance can
also be graphite, which has a giant covalent structure.
Experiment 9.3
Class practice 9.5
9.7 Predicting structures from physical properties
P. 59 / 73
Experiment 9.3
9.8 Predicting physical properties from
bonding and structure
The physical properties of a substance are closely
related to its bonding and structure.
From the group numbers of the elements that
make up a substance, we can predict the bonding
and structure of the substance.
Example 9.2
Class practice 9.6
P. 60 / 73
9.9 Applications of substances according
to their properties
Substances with the same structure have some
general properties.
They also have some characteristic properties
of their own.
Reading to learn
STSE connections 9.1
P. 61 / 73
Key terms
1.
2.
3.
4.
5.
6.
7.
8.
9.
giant covalent structure 巨型共價結構
giant ionic structure 巨型離子結構
giant metallic structure 巨型金屬結構
giant structure 巨型結構
intermolecular force 分子間引力
macromolecule 巨大分子
molecular structure 分子結構
simple molecular structure 簡單分子結構
van der Waals’ force 范德華力
P. 62 / 73
Progress check
1. How can we classify substances according to
structures?
2. What structure do carbon dioxide and iodine
have? How are the molecules in carbon dioxide
and iodine arranged in this structure?
3. What are van der Waals’ forces? Where do they
exist?
4. How are the properties of substances with
simple molecular structure related to their
structures and bonding?
P. 63 / 73
5. What structure do diamond, graphite and quartz
have? How are the atoms in diamond, graphite
and quartz arranged in this structure?
6. How are the properties of substances with a giant
covalent structure related to their structures and
bonding?
7. What structure do sodium chloride and caesium
chloride have? How are the ions in sodium
chloride and caesium chloride arranged in this
structure?
8. How are the properties of ionic compounds
related to their structures and bonding?
Progress check
P. 64 / 73
9. What structure do metals have? How are the metal
atoms arranged in this structure?
10. What are the similarities and differences between
structures and properties of substances with
simple molecular, giant covalent, giant ionic and
giant metallic structures?
11. How can we deduce the structures and bonding of
substances from their physical properties?
12. How can we deduce the physical properties of
substances from their structures and bonding?
13. How are the applications of substances related to
their properties?
Progress check
P. 65 / 73
Summary
9.1
Structures of substances
1.
The structure of a substance is a description of
what its constituent particles are, and how they
are arranged or packed together.
2.
All substances exist as either molecular
structures or giant structures under ordinary
conditions.
P. 66 / 73
9.2
Simple molecular structures
3.
In substances with a simple molecular structure,
atoms within a molecule are bonded together
by strong covalent bonds and each molecule is
attracted to neighbouring molecules by weak
intermolecular forces.
9.3
4.
Giant covalent structures
In a few elements and compounds, the nonmetal atoms are joined together by covalent
bonds to form a giant network called giant
covalent structure.
Summary
P. 67 / 73
9.4
5.
Giant ionic structures
In ionic compounds, crystals consisting of
positive and negative ions are held together by
strong non-directional electrostatic attractions.
The ions are regularly packed to form a
continuous, three-dimensional giant ionic
structure.
9.5
6.
Giant metallic structures
Metal ions are joined to one another in a giant
metallic structure by metallic bonds, which
result from the attraction between a ‘sea’ of
delocalized electrons and metal ions.
Summary
P. 68 / 73
9.6
Comparison of structures and properties of
substances
7.
The structure, bonding and physical properties
of substances with simple molecular structure,
giant covalent structure, giant ionic structure and
giant metallic structure are summarized in Table
9.2.
9.7
8.
Predicting structures from physical properties
It is possible to predict the structure of a
substance from its physical properties.
(Refer to the flow chart in Figure 9.19.)
Summary
P. 69 / 73
9.8
9.
9.9
10.
Predicting physical properties from bonding
and structure
It is possible to predict the physical properties of
a substance from its bonding and structure.
(Refer to Example 9.2.)
Applications of substances according to their
properties
Some specialized new materials have been
created on the basis of the findings of research
on the structure, chemical bonding, and other
properties of matter.
Summary
P. 70 / 73
Concept map
SUBSTANCES
Molecular structures
Giant
________
structures
Macromolecules
examples
Simple
molecular
structures
Giant
Giant
Giant
Compounds
_______ _______
metallic
covalent
ionic
_______
e.g.
polyethene structures structures structures
P. 71 / 73
Simple
molecular
structures
discrete molecules are
attracted by
Intermolecular
forces
examples
Elements
I2
e.g. H2, ______
Compounds
CO2
e.g. H2O, _____
Concept map
P. 72 / 73
Giant ______
ionic
structures
positively charged
ions and negatively
charged ions packed
regularly by
Ionic bond
Concept map
metal
atoms are
held
together by
all atoms
are bonded
together by
Covalent bond
Metallic bond
examples
examples
Compounds
e.g.
MgO
NaCl, _____
metallic
Giant _______
structures
covalent
Giant ________
structures
Elements
e.g.
diamond,
graphite
_________
examples
Compounds
e.g. SiO2
P. 73 / 73
Elements
e.g. Fe, Cu