The Alkanes

The Alkanes

We will start with the simplest homologous series called the Alkanes. As with all homologous series, the members of the series all have things in common and vary in a defined way. Each member of the Alkane series has carbon- hydrogen single bonds only. They are called saturated compounds because of this.

All homologous series has a general formula. This is the common relationship between the number of carbons and the number of hydrogen in subsequent members of the series.

The general formula for the alkanes is CnH2n+2. Where n is the number of carbon atoms ranging from 1 upwards.

Molecular formula
N=1 CH4
N=2 C2H6
N=3 C3H8

As you can see the first member of the series is CH4, the second member is C2H6 and etc. There can possibly be any number of carbon atoms however we will focus on the first 10 members of the series which is shown below. You should also note that each member of the series ends with the suffix –ane.

  • CH4–       Methane
  • C2H6 –    Ethane
  • C3H8 –    Propane
  • C4H10–    Butane
  • C5H12–    Pentane
  • C6H14–    Hexane
  • C7H16–    Heptane
  • C8H18–    Octane
  • C9H20–    Dudecane
  • C10H22–   Decane

The prefixes below are commonly used in organic chemistry and it will aid you in name organic compounds if you learn these prefixes.

Meth-   1 carbon atom

Eth-        2 carbon atoms

Prop-     3 carbon atoms

But-       4 carbon atoms

Pent-     5 carbon atoms

Hex-      6 carbon atoms


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