Silicon(IV) Oxide
Section: 2. Atoms, Elements & Compounds | Syllabus: Cambridge IGCSE Chemistry (0620)
Structure of Silicon(IV) Oxide
Silicon(IV) oxide (silicon dioxide, SiO₂) is the main component of sand and quartz. Like diamond, it has a giant covalent structure - but built from two elements instead of one.
- Each silicon atom forms 4 covalent bonds to 4 oxygen atoms, in a tetrahedral arrangement
- Each oxygen atom bridges and bonds to 2 silicon atoms
- This continues throughout the crystal as one giant 3D network - the formula SiO₂ shows only the 1:2 ratio of Si to O atoms, not a separate molecule
Every oxygen atom bridges two silicon tetrahedra, linking the whole crystal into one continuous covalent network
Properties of Silicon(IV) Oxide
| Property | Silicon(IV) oxide | Explanation |
|---|---|---|
| Melting point | Very high (1710°C) | Many strong Si-O covalent bonds must be broken throughout the giant structure |
| Hardness | Very hard | Rigid 3D network of covalent bonds in every direction |
| Electrical conductivity | Does not conduct | All outer electrons are used in covalent bonds - none are free to move |
Uses include glass and ceramics manufacture (from sand), and electronics (quartz crystals in clocks and oscillators).
Similarity Between Silicon(IV) Oxide and Diamond
Silicon(IV) oxide and diamond share very similar properties (both very high melting points, very hard, non-conductors) because they share the same type of structure: a giant covalent network held together by strong covalent bonds acting in every direction, with no free electrons or ions.
Worked Example: Explaining the Similarity
- Question: silicon(IV) oxide and diamond have similarly very high melting points. Explain why, in terms of their structures. [2]
- Answer: both substances have a giant covalent structure, with strong covalent bonds extending throughout the whole structure in three dimensions [1]; a very large amount of energy is needed to break these many strong bonds, so both have very high melting points [1]
Common Mistakes
- ❌ Thinking SiO₂ is ionic because it looks like a metal-plus-non-metal formula
- ✓ silicon is a metalloid, not a metal - silicon and oxygen share electrons in strong covalent bonds, forming a giant covalent structure, not an ionic one
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