The alkanes are a class of hydrocarbons that contain only single bonds.  Because they contain single bonds only, alkanes are classified as "saturated".  

 A homologous series is a progression of organic compounds that differ only in the number of repeating units.   In the homologous series shown in the animation below, each alkane has one more CH₂ group than the preceding alkane. Keep clicking on the arrow to see the various compounds included in this homologous series.

First Ten Alkanes

Did you notice a pattern between the number of carbon atoms and the number of hydrogen atoms?  The general formula for an alkane is C_nH_2n+2.  Knowing this pattern can help you identify the family to which a hydrocarbon belongs. This is quite handy for large molecules.  For example, is the compound with the molecular formula C₁₇H₃₆ an alkane? The answer is yes!

Note that some alkanes form cyclical structures called cycloalkanes.  In these structures, the carbon chain forms a closed ring.  Study the examples below depicting cyclopentane  and cyclohexane.  Count the carbons and hydrogens in each molecule.  What do you notice about these molecular formulae?  Do they fit the regular pattern for alkanes?

Although these compounds are classified as saturated, they have a different general formula than other alkanes.  Instead of C_nH_2n+2, they have the general formula C_nH_2n.  Can you see why the general formula of cycloalkanes shows two less hydrogen per molecule?