The Alkane Series: Building Them From ScratchThe alkanes are a series of simple molecules that are built solely from Carbon and Hydrogen. We already know that Carbon has 4 electrons in its outer shell and Hydrogen has 1, and this is what gives us the following electron dot diagrams:
Note that Carbon is stable with 8 electrons in its outer shell whereas Hydrogen requires only 2 electronsfor stability. Using just these two elements we will now construct carbon chains ranging from 1 to 10 carbon atoms bonded together. The Hydrogen atoms will be used to take up any gaps left over after the carbon atoms are joined. A sheet of these electron dot diagrams is available here for free download in PDF form. You can print them and cut them up, or use a program like Paint or Photoshop to move the atoms around to make the same structures presented here. All the following alkanes are built using this simple 4 step process. Step 1: Take the correct number of carbon atoms and a bunch of Hydrogen atoms; just use as many Hydrogens as you need. Step 2: Join the Carbon atoms together using just a single pair of electrons, and place Hydrogens around the outside, one for every unused electron on the Carbon atoms. Step 3: Move the Hydrogens in to make the electron pairs on the unused Carbon electrons. Step 4: Replace pairs of electrons with lines joining the atoms sharing the pair. This gives each Carbon 8 electrons and each Hydrogen 2. Following this simple method it is possible to generate infinitely long molecules made of Carbon and Hydrogen. The single Carbon atom has no other Carbons to share electrons with. That leaves its four vacant slots open to be occupied by Hydrogen atoms. The result is the molecule we call Methane that has the chemical formula CH4.
Two Carbon Atoms: Ethane The diagram below shows the construction of Ethane. Step one shows more than necessary Hydrogen atoms; this is simply to demonstrate that all you need do is use as many as you need, and not start with a definite number. Ethane is an essential resource for the plastics industry as well as a fuel source.
Three Carbon Atoms: Propane Following the same process as for Methane and Ethane, we can build the 3 Carbon molecule Propane. Propane is an important fuel and is sometimes touted as an alternative fossil fuel due to its use, along with Butane, in LPG powered vehicles.
Now that we see how these molecules are put together, we can rapidly construct the remaining molecules containing between 4 and 10 Carbon atoms, as follows:
The series goes on indefinitely in theory, and in practice molecules with many hundreds of Carbon atoms can be found. The members of the alkane series are a vital contributor to our current energy supply as they are the main constituent of oil and natural gas. Return from The Alkane Series to Solar Chemistry 2 or return to the Green Planet home page for more Solar Power Facts.
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