Giant covalent structures: connections continue through the solid
| English | Français |
|---|---|
| silicon dioxide/ˈsɪlɪkən daɪˈɒksaɪd/ | dioxyde de silicium |
| giant covalent structure/ˈdʒaɪənt ˈkəʊvələnt ˈstrʌktʃə/ | structure covalente géante |
What would explain this observation?
- A drawing showing one silicon atom bonded to four oxygens is only a local piece of silica. The oxygen bridges continue into a network, so the pictured fragment is not a separate SiO₄ molecule.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Diamond, graphite and silicon dioxide 二氧化硅 have giant covalent structures 巨型共价结构. Strong covalent bonds join atoms through large repeating structures, rather than a substance made of small independent molecules. Many strong covalent bonds must be overcome to melt these structures, requiring much energy and producing very high melting points. They are solids under ordinary conditions.
- giant covalent structure: An extended network of atoms connected by strong covalent bonds; silicon dioxide: A substance with a giant covalent structure and overall silicon-to-oxygen ratio 1:2.
Why does silica have a very high melting point?
In silicon dioxide, each silicon is linked to four oxygens and each oxygen bridges two silicons, producing the overall Si:O ratio 1:2. A local drawing may show four surrounding oxygens because each is shared with another silicon elsewhere in the network. Graphite has strongly bonded layers but weaker attractions between layers; its high-temperature behaviour and layer sliding concern different connections.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- In silicon dioxide, each silicon is linked to four oxygens and each oxygen bridges two silicons, producing the overall Si:O ratio 1:2. A local drawing may show four surrounding oxygens because each is shared with another silicon elsewhere in the network. Graphite has strongly bonded layers but weaker attractions between layers; its high-temperature behaviour and layer sliding concern different connections.
- Trace bonds from one atom to its neighbours and then onward beyond the fragment. Distinguish an uninterrupted network from separate groups with gaps between them. Compare a local coordination drawing and the bulk formula. Models may omit remote bonds, distort angles or enlarge spaces; explain what the representation does and does not establish.
Which two habits make the investigation or model in this case more defensible?
Trace bonds from one atom to its neighbours and then onward beyond the fragment. Distinguish an uninterrupted network from separate groups with gaps between them. Compare a local coordination drawing and the bulk formula. Models may omit remote bonds, distort angles or enlarge spaces; explain what the representation does and does not establish.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: a stated representative silica region contains twelve silicon atoms and twenty-four oxygen atoms. The ratio 12:24 reduces to 1:2, giving SiO₂. It is a ratio in a continuing structure, not proof of twelve independent SiO₂ molecules. A local four-oxygen coordination shell cannot be counted without the sharing information to infer the bulk formula.
A representative silica region contains 18 silicon atoms. At the Si:O ratio 1:2, how many oxygen atoms does it contain? Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A representative silica region contains 18 silicon atoms. At the Si:O ratio 1:2, how many oxygen atoms does it contain?
The result is 36 atoms. Known: a stated representative silica region contains twelve silicon atoms and twenty-four oxygen atoms. The ratio 12:24 reduces to 1:2, giving SiO₂. It is a ratio in a continuing structure, not proof of twelve independent SiO₂ molecules. A local four-oxygen coordination shell cannot be counted without the sharing information to infer the bulk formula.
Check the conclusion and its limits
- Giant structure does not mean giant individual atoms. Melting a covalent network differs from boiling a small molecular substance because the relevant connections differ. Not all giant covalent substances are electrical insulators: graphite is a key exception with delocalised electrons.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
The four oxygens around one silicon mean the bulk silica formula must be SiO₄. This claim is false: Giant structure does not mean giant individual atoms. Melting a covalent network differs from boiling a small molecular substance because the relevant connections differ. Not all giant covalent substances are electrical insulators: graphite is a key exception with delocalised electrons.
Giant covalent structures: connections continue through the solid: In silicon dioxide, each silicon is linked to four oxygens and each oxygen bridges two silicons, producing the overall Si:O ratio 1:2. A local drawing may show four surrounding oxygens because each is shared with another silicon elsewhere in the network. Graphite has strongly bonded layers but weaker attractions between layers; its high-temperature behaviour and layer sliding concern different connections.
The four oxygens around one silicon mean the bulk silica formula must be SiO₄.
Giant structure does not mean giant individual atoms. Melting a covalent network differs from boiling a small molecular substance because the relevant connections differ. Not all giant covalent substances are electrical insulators: graphite is a key exception with delocalised electrons.
An extended network of atoms connected by strong covalent bonds: write the technical term.
giant covalent structure means An extended network of atoms connected by strong covalent bonds.