Saturated vs. unsaturated hydrocarbons
A hydrocarbon is saturated if it contains no double or triple bonds. If either of these is present in a compound, this will make it unsaturated. Figure 1 shows a visual representation of this principle.
Figure 1. Overview of saturated vs. unsaturated compounds.
The molecular formula of a non-cyclic alkane will follow this rule for the number of carbons and hydrogens: CnH2n+2.
Non-cyclic alkenes follow this rule: CnH2n.
Non-cyclic alkynes follow this rule: CnH2n-2.