# How do you classify alkanes, alkenes and alkynes?

By their $\text{degree of unsaturation}$. A saturated species, an alkane, has general formula ${C}_{n} {H}_{2 n + 2}$.
The formula ${C}_{n} {H}_{2 n + 2}$ is important. Try it for hexanes, $n = 6$, heptane, $n = 7$, methane. Are the formulae consistent?
Of course halogens substitute for hydrogen, i.e. ${C}_{n} {H}_{2 n + 1} X$. Each $2$ hydrogens less than the saturated formula, ${C}_{n} {H}_{2 n + 2}$ corresponds to an olefinic bond, i.e. $C = C , C = N , C = O$, OR a ring junction. Is it consistent for cylcohexane?
For compounds containing nitrogen, subtract $N H$; try it for prussic acid, $H C \equiv N$, clearly 3""^@ of unsaturation. The degree of unsaturation is a very useful parameter to characterize an organic formula. An example is one of the simplest organic molecules, ${C}_{6} {H}_{6} ,$ benzene. Given my spray, this has 4 degrees of unsaturation. And indeed benzene has the equivalent of $3$ $\text{double bonds}$ and a ring. Try this treatment with toluene, acetone, ethylene, acetylene, as well as say decane, and decene, and cyclohexane. If you have any queries, state them here.