What are the three types of covalent substance, based on their structure?
- Substances made of small, separate molecules
- Substances made of very large molecules
- Giant covalent structures
AQA GCSE Combined Science: Trilogy (8464) — Chemistry — Foundation · 5.2.1.4
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What are the three types of covalent substance, based on their structure?
What does each chemical formula represent in a substance made of small, separate molecules?
One discrete molecule.
What is the structure of a polymer molecule?
A long covalent chain of many atoms, made from repeating units.
How does bonding in a giant covalent structure differ from bonding in a molecular substance?
Covalent bonds extend through a continuous network rather than forming separate molecules.
What are two examples of giant covalent structures?
Diamond and silicon dioxide.
What does a chemical formula show?
The elements in a substance and the relative numbers of their atoms, using element symbols and subscripts.
What does a molecular formula show?
The type and number of each atom in one molecule.
How can you deduce the formula of a simple compound from a model or diagram?
Identify the different atoms and their relative numbers, then use the corresponding element symbols and subscripts.
What diagram features identify a giant covalent structure?
A repeating, extended network of atoms joined by covalent bonds, rather than separate individual molecules.
How does diamond appear in a structure diagram?
A three-dimensional network of carbon atoms.
How does graphite appear in a structure diagram?
Layers of carbon atoms bonded in extended sheets.
How does silicon dioxide appear in a structure diagram?
A network of silicon and oxygen atoms linked throughout the structure.
What does a polymer repeat-unit diagram represent?
A section of a long covalent polymer chain, not a separate small molecule.
What do bonds extending through the brackets of a polymer repeat-unit diagram show?
The unit connects to neighbouring units in the chain.
What does represent in polymer repeat-unit notation?
The number of repetitions of the unit; it is a large number.
What does a single bond line in a polymer repeat-unit diagram represent?
A strong covalent bond formed by a shared pair of electrons.
What is the structure of the poly(ethene) repeat unit?
Two carbon atoms joined by a single bond, with two hydrogen atoms bonded to each carbon.