9cM.02/03 Macromolecuar
Thursday, 10 April 2025
Lesson objective(s):
 I will be able to draw giant lattice structures
 They are the result of large covalent bonding
Starter:
Draw the ionic compound for NaF
Key
words:
Electrons,
ions,
share
Properties for Covalent bonding
Strong Covalent Bonds (not broken)
Molecular covalent substances
show weak INTERMOLECULAR
FORCES between molecules.
…so these substances have low
melting and boiling point.
As a result, these are liquid or gas
at room temperature.
They don’t have free moving
electrons, so they do not conduct
electricity.
Strong Covalent Bonds (not broken)
The term ‘Lattice structure’ are used for the following:
1) Ionic bonding
2) Covalent bonding
3) Metallic bonding
State that there are several different forms of carbon, including diamond
and graphite
Giant covalent structures - MACROMOLECULES
Some substances are
covalent as they are
made of non-metals
but show different
structures:
Lattices
Large molecules
Diamond and graphite
are allotropes.
Describe the giant covalent structures of graphite and diamond
a) Diamond (made of carbon atoms)
(i) Carbon is in Group IV and has 4
unpaired electrons
(ii) 1 Carbon atom is covalent bonded to 4
Carbon atoms in a tetrahedral
arrangement
(iii) 3 properties:
 very hard
 high melting point
 does not conduct electricity since there
are no free moving electrons as they
are all used in bonding
Describe the giant covalent structures of graphite and diamond
 Drawing diamond in an exam
Description of bonding in diamond
Each carbon atom is covalently
bonded to four other carbon atoms in
a tetrahedral arrangement.
Property(ies): very hard
Use(s): drilling and cutting
b) Graphite (another form or allotrope of carbon)
(i) 1 carbon atom is covalently bonded
to 3 other carbon atoms in a
hexagonal arrangement
Strong Covalent Bond
(ii) (a) Arranged layers held together
by weak forces of attraction (1 mark)
(b) the layers can slider over each
other (1 mark) when a force is applied
Between these layers are free moving
electrons meaning it can conduct
electricity – delocalised electron(s)
Weak INTERMOLECULAR FORCES of attraction
b) Graphite (another form or allotrope of carbon)
 It does however have a very high melting point since all the strong
covalent bonds between the atoms have to be broken for it to change
state requiring lots of energy. (Graphite actually sublimes)
Property
Conducts electricity
Soft
Use
electrodes in electrolysis
(conductor)
Lubricant
Diamond
1 x Carbon atom covalent
bonding to 4 x Carbon atoms
Tetrahedral structure
Strong covalent bonds between
atoms
No delocalised electrons
Non-conductor
Hard
Drill bits
Graphite
1 x Carbon atom covalent
bonding to 3 x Carbon atoms
Hexagonal layer
Weak IMF of attraction between
layers (layers can slide off)
Delocalised electrons
Conductor
Soft
Lubricant, conductor
Describe the macromolecular structure of silicon(IV) oxide (silicon dioxide,
SiO2)
 Each silicon atom is covalently bonded
(1) to four oxygen atoms (1) & each
oxygen atom is covalently bonded to
(1) two silicon atoms in a tetrahedral
arrangement (1) = 4 marks
 Silicon (IV) oxide not only has a similar
structure to diamond but also has
similar properties
 It is hard, has a high melting point and
does not conduct electricity
CIE Cambridge Learner Book Page 75
1) How is an ionic bond different from a covalent bond? (2 marks)
Ionic bond – An ionic bond is formed when at atom lose or gain
electrons (1). Covalent bond –the atoms share electrons (1).
2) When a metal joins with a non-metal, is a covalent or an ionic
compound made? (1 mark)
Ionic bond (1)
3) Oxygen atoms join together to for an Oxygen molecule. Explain
what the word molecule means. (2 marks)
A particle with more than one atom (1)
The atoms share at least one covalent bond (1)
4) What is a macromolecule? Give an example. (2 marks)
A giant lattice structure (1), Silicon dioxide / diamond / Graphite (1)
Covalent & Ionic Compounds – the differences in M.P & B.P.
Covalent
Ionic
Simple molecule has strong
Covalent bond BETWEEN the
atoms. HIGH MP & BP
A strong electrostatic forces of
attraction between the cation &
anion. HIGH MP & BP
A lot of thermal energy is
required to break the bond(s)
Simple molecule has weak IMF
bond BETWEEN the molecules.
LOW MP & BP
A lot of thermal energy is
required to break the bond(s)
A small amount of thermal
energy is required to break the
bond(s)
CIE Cambridge Learner Book Page 76
5) Is Magnesium chloride an ionic compound or a simple molecule
with covalent bonds? Give reason(s) for your answer. (2 marks)
Ionic as it has a high MP & BP (1) The compound is made from a
metal ion & non-metal ion (1)
6) Is Ammonia an ionic compound or a simple molecule with
covalent bonds? Give reason(s) for your answer. (1 mark)
Covalent due to two non-metals sharing the electrons.
7) Is Ammonia a solid, liquid or gas at room temperature? (1 mark)
A gas
8) Why do Magnesium chloride & Calcium oxide have high MP? (5
marks)
They are ionic compounds (1). They possess a strong electrostatic
forces of attraction (1) between cation & anion (1) in a regular lattice
structure (1). A lot of thermal energy is needed to break the bonds
(1)
CIE Cambridge Learner Book Page 76
9) Why do Methane & Chlorine have low melting points? (3 marks)
They are simple molecules (1)
They have weak Intermolecular forces of attraction between the
molecules (1) so less energy is needed to melt them (1)
10) Look at the picture of the Copper sulfate crystals. What sort of
chemical bonds does this substance have? Give reason(s) for your
answer. (3 marks)
Ionic bonding (1). It is
made up of cations &
anions (1). It has formed a
giant crystal structure (1).
CIE Cambridge Learner Book Page 77
11) A substance has a M.P. of 3087OC & a B.P. 4300OC. What sort of
chemical bonds does it have. Give a reason for your answers.
Ionic Bonds due to the high Melting Points & high Boiling Points.
12) Silicon dioxide (SiO2) is a compound formed from two nonmetals, Silicon & Oxygen. It is the chemical name for sand. It is a hard
substance with a melting point of 1610OC. Which properties of
Silicon dioxide suggest that it has a giant covalent structure. (4
marks)
Each silicon atom is covalently bonded (1) to four oxygen atoms (1) &
each oxygen atom is covalently bonded to (1) two silicon atoms in a
tetrahedral arrangement (1)
Conduct Electricity
Ionic
Covalent
Solid – cannot connect
electricity
Simple molecule – does not
conduct electricity
Melted – free moving ions &
delocalised (free moving)
electrons
Macromolecular (giant
covalent) – Graphite. Due to
delocalised electrons between
the layers.
Aqueous – dissolved in water.
Free moving ions & delocalised
(free moving) electrons