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IGCSE Chemistry Notes Giant covalent structures

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Macromolecules

Giant covalent structures of Diamond/Graphite/Silicon(IV) oxide

Overview

  • Macromolecules are giant covalent structures
  • They have a rigid three dimensional network of strong covalent bonds throughout the crystal.
  • It takes a lot of energy to break the bond
  • They have very high boiling and melting points.
  • Example of giant covalent structures are: Graphite, diamond and [Silicon(IV) oxide-also called as silicon dioxide]

macromolecules-igcse-chemistry 

Diamond and Silicon

Diamond igcse-chemistry-diamond-notes

 

Silicon Dioxideigcse-chemistry-silicon-dioxide-notes

  Diamond Silicon Dioxide
Structure    
Bonding One carbon atom is bonded to 4 other carbon atoms and no electrons are set free. One silicon atom is bonded to 3 other oxygen atoms and no electron is set free.
Electrical Conductivity Does not conduct electricity as it does not have any delocalised electrons Does not conduct electricity as it does not have any delocalised electrons
Melting and boiling point High-because a lot of energy is needed to break the strong covalent bonds. High-because a lot of energy is needed to break the strong covalent bonds.
Hard Very hard-It can't be scratched easily Very hard-It can't be scratched easily
Colour Colourless Colourless

Graphite

  • Graphite is a black shiny solid.
  • It's carbon atoms are arranged in layers.
  • Every layer consists of carbon atoms in hexagonal ring.
  • Each carbon atom is covalently bonded to 3 other carbon atoms and one electron is set free. Thus in the entire lattice there is a sea of delocalised electrons. Hence graphite conducts electricity because the delocalised electrons can drift along the layers when voltage is applied. As graphite conducts electricity , it is used to make electrodes for electrolysis.
  • Graphite has a slippery feel as the bonding between the layers in graphite is weak. hence the layers can slide past each other. Hence it has a slippery feel.
  • The layers of graphite can flake off because of this weak bonding. hence it is used as a lubricant and in pencil lead
 

Syllabus Objectives

CORE:

  • Describe the giant covalent structures of graphite and diamond
  • Relate the structures and bonding of graphite and diamond to their uses, limited to:
  • (a) graphite as a lubricant and as an electrode
  • (b) diamond in cutting tools

EXTENDED:

  • Describe the giant covalent structure of silicon(IV) oxide, SiO2
  • Describe the similarity in properties between diamond and silicon(IV) oxide, related to their structures

Revision Notes

IGCSE Chemistry Notes Giant Covalent Structures Revised Syllabus

 

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Topic: Giant Covalent Structures / Test your Understanding

Click the highlighted blanks to reveal the correct answer.

1 What are Giant Covalent Structures?

1. A giant covalent structure is a large
________________ network
of atoms joined by
________________ covalent bonds
.
2. Giant covalent structures have very
________________ high
melting and boiling points.
3. A large amount of
________________ energy
is required to break the covalent bonds.
4. Examples include
________________ diamond
,
________________ graphite
, and
________________ silicon(IV) oxide
.

2 Diamond

5. Diamond is made entirely of
________________ carbon
atoms.
6. Each carbon atom forms
________________ four
covalent bonds.
7. Diamond has a giant
________________ three-dimensional
structure.
8. Diamond does not conduct electricity because it has no
________________ free electrons
.
9. Diamond is extremely
________________ hard
.
10. Diamond is used in
________________ cutting tools
.

3 Graphite

11. In graphite, each carbon atom forms
________________ three
covalent bonds.
12. Graphite atoms are arranged in
________________ layers
.
13. One electron from each carbon atom is
________________ delocalised
.
14. Graphite can conduct
________________ electricity
.
15. The layers are held together by
________________ weak forces
.
16. Graphite is used as a
________________ lubricant
.
17. Graphite is used as an
________________ electrode
in electrolysis.

4 Silicon(IV) Oxide (SiO2)

18. Silicon(IV) oxide is also called
________________ silica
.
19. Its chemical formula is
________________ SiO?
.
20. Each silicon atom bonds to
________________ four
oxygen atoms.
21. Silicon dioxide forms a giant
________________ three-dimensional
network.
22. Silicon dioxide does not conduct electricity because it has no
________________ free electrons
.

5 Similarities Between Diamond and Silicon(IV) Oxide

23. Both have
________________ giant covalent
structures.
24. Both have very
________________ high melting points
.
25. Both do not conduct
________________ electricity
.

6 Summary Review

26. Graphite conducts electricity because it contains
________________ delocalised electrons
.
27. Diamond does not conduct electricity because it has no
________________ free electrons
.
28. Graphite layers slide because they are held by
________________ weak forces
.
29. Diamond is used in cutting tools because it is extremely
________________ hard
.
30. Silicon(IV) oxide forms a giant covalent
________________ lattice
.

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IGCSE Chemistry Revised Syllabus Notes[ 2023-2025 exams]

1-States of matter

2 Atoms, elements and compounds

3 Stoichiometry

4 Electrochemistry

5 Chemical energetics

6 Chemical reactions

7 Acids, bases and salts

8 The Periodic Table

9 Metals

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10 Chemistry of the environment

11 Organic chemistry

12 Experimental techniques and chemical analysis