Silicon(IV) Oxide (Cambridge International IGCSE Chemistry)

Structure of silicon(IV) oxide

Spec point — 2.4.2 · Describe the giant covalent structure of silicon(IV) oxide, SiO2

What is the structure of silicon(IV) oxide?

Extended tier only

• Silicon(IV) oxide (also known as silicon dioxide or silica), SiO₂, is a macromolecular compound which occurs naturally as sand and quartz
• Each oxygen atom forms covalent bonds with 2 silicon atoms and each silicon atom in turn forms covalent bonds with 4 oxygen atoms
• A tetrahedron is formed with one silicon atom and four oxygen atoms, similar to diamond

The structure of silicon(IV) oxide

Diagram showing the structure of SiO₂with the silicon atoms in blue and the oxygen atoms in red

Comparing diamond & silicon(IV) oxide

Spec point — 2.4.2 · Describe the similarity in properties between diamond and silicon(IV) oxide, related to their structures

How does diamond compare to silicon(IV) oxide?

Extended tier only

• SiO₂ has lots of very strong covalent bonds and no intermolecular forces so it has similar properties to diamond
• It is very hard, has a very high boiling point, is insoluble in water and does not conduct electricity
• SiO₂ is cheap since it is available naturally and is used to make sandpaper and to line the inside of furnaces