9.10C - Drawing and naming the first four alkanes
Learn the names and molecular formulae of the first four alkanes, then use carbon’s four-bond rule to draw and check their displayed structures. This is a separate Chemistry point.
Names and molecular formulae
A molecular formula gives the number of atoms of each element in one molecule. For example, means three carbon atoms and eight hydrogen atoms.
| Alkane | Carbon atoms | Molecular formula |
|---|---|---|
| methane | 1 | |
| ethane | 2 | |
| propane | 3 | |
| butane | 4 |
The prefixes meth-, eth-, prop- and but- indicate one, two, three and four carbon atoms. Learn the name–formula pairs so you can recall them without a supplied table. Each successive molecule in this list has one more carbon and two more hydrogen atoms.
Reading displayed structures
Displayed structure
A displayed structure shows every atom and every covalent bond in a molecule.
In an alkane, each bond is single and is shown by one line. Every carbon has four bond lines and every hydrogen has one. A molecular formula gives atom counts; a displayed structure also shows how the atoms are joined.
[DIAGRAM: asset_name: first_four_alkane_displayed_structures - diagram 1; asset_slug: 214_9_10c_formulae_and_structures_of_the_first_four_alkanes_diagram1; file: 214_9_10c_formulae_and_structures_of_the_first_four_alkanes_diagram1_imagegen_v1.png; recommended_method: deterministic_drawn; description: Deterministic monochrome displayed-structure reference for methane CH4, ethane C2H6, propane C3H8 and butane C4H10. Exact labels required: Methane CH4, Ethane C2H6, Propane C3H8, Butane C4H10, and "each line = one covalent bond". Structures must show all C-H and C-C covalent bonds as single lines: methane has one carbon bonded to four hydrogens; ethane is two carbon atoms joined, with each carbon bonded to three hydrogens; propane is CH3-CH2-CH3 with every C-H bond shown; butane is CH3-CH2-CH2-CH3 with every C-H bond shown. This is an assessed/exact visual generated deterministically in NovaLearn monochrome style; nearby prose provides the formulae and bond-counting checks for accessibility.]
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