Carbon skeletons: chains, names and isomers

A saturated chain contains only $\ce{C-C}$ single bonds: these are the alkanes, of formula $\text{C}_n\text{H}_{2n+2}$ when they are not cyclic. An unsaturated chain carries at least one $\ce{C=C}$ double bond (alkenes, $\text{C}_n\text{H}_{2n}$) or one $\ce{C#C}$ triple bond (alkynes, $\text{C}_n\text{H}_{2n-2}$). There is no free rotation about a double bond.