Learning focus
Develop precise chemical language, connect particle and bonding models to observations, interpret diagrams and data, and apply ideas to unfamiliar examples.
Network
Silicon(IV) oxide, SiO2, has a giant covalent network. Each silicon bonds to oxygen atoms and each oxygen bridges silicon atoms. The formula shows a 1:2 ratio, not a small molecule.
High melting point
Many strong Si-O bonds extend throughout the structure. Considerable energy is required to break enough bonds for melting.
Hardness
The rigid network prevents easy movement of atoms and gives hard materials such as quartz.
Conductivity
There are no mobile ions or delocalised electrons under ordinary conditions, so silicon(IV) oxide does not conduct electricity.
Comparison with diamond
Both are hard, high-melting, giant covalent solids and poor conductors. Their atom types and detailed networks differ.
Practical or data skill
Compare data for diamond and silicon dioxide and identify the shared structure-property explanation.
Examination tip
Do not draw SiO2 as separate O=Si=O molecules.
Review questions and suggested answers
Question 1
Why high melting point?
Suggested answer
Many strong covalent bonds must be broken.
Question 2
Does SiO2 conduct?
Suggested answer
No.
Question 3
One similarity with diamond?
Suggested answer
Both are hard giant covalent solids with high melting points.
