Final answer:
The first 20 alkanes each have a molecular, a semi-developed (condensed), and a skeletal formula, with the molecular formula having a general pattern of CnH2n+2. The names indicate the number of carbon atoms and always end in '-ane' for alkanes.
Step-by-step explanation:
The formulas for the first 20 straight-chain alkanes include the molecular, developed (also known as the expanded structural), semi-developed (or condensed structural), and skeletal formulas. The name of an alkane generally indicates how many carbon atoms are in the molecule, with the prefix (meth-, eth-, prop-, but-, etc.) indicating the number of carbons, and the suffix (-ane) indicating it's an alkane. Here, we'll develop the formulas for the first four as an example:
- Methane: Molecular - CH4, Semi-developed - CH4, Skeletal - C
- Ethane: Molecular - C2H6, Semi-developed - CH3CH3, Skeletal - C-C
- Propane: Molecular - C3H8, Semi-developed - CH3CH2CH3, Skeletal - C-C-C
- Butane: Molecular - C4H10, Semi-developed - CH3(CH2)2CH3, Skeletal - C-C-C-C
To complete the list for the first 20 alkanes, this pattern continues, adding one CH2 unit for each new member of the series. The molecular formula of alkanes follows a general pattern of CnH2n+2, where 'n' is the number of carbon atoms.