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Identifying Alkanes and Hydrocarbons

Hydrocarbons are made solely of hydrogen and carbon. Alkanes are a subcategory of hydrocarbons where each carbon is bonded to either another carbon or a hydrogen by single bonds. Saturated hydrocarbons have the maximum number of hydrogen atoms, that value is 2n + 2 (n = number of carbons). Alkanes are always hydrocarbons, saturated hydrocarbons are always alkanes.

>> Example 1

Classify each of the following as a hydrocarbon, alkane or saturated hydrocarbon. (Note: more than one of these or none of these might be correct).

1. C₂H₆
2. C₆H₆
3. CH₃CH₂CH₂CH₃
4. 

Solution:

1. Saturated hydrocarbon and alkane. The substance contains only hydrogen and carbon, so it is a hydrocarbon. 2(2) + 2 = 6; therefore it is saturated. Since all saturated hydrocarbons are alkanes, this is also an alkane.
2. Hydrocarbon only. Although made only of hydrogen and carbon, there are fewer hydrogens than needed for the substance to be saturated. There is no way to draw this structure without using double (or triple) bonds, so it is not an alkane.
3. Saturated hydrocarbon and alkane. If you drew out this structure it would be all single bonds. It also has 10 hydrogens and four carbons. 2(4) + 2 = 10, so it is saturated.
4. Alkane and hydrocarbon. This structure consists of only single bonds but has only 10 hydrogens. A saturated structure would have 2(5) + 2 = 12.

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