Here is how I would approach the problem of drawing two structures for the compound C₂H₆O.

Given the Lewis structures of the atoms

and the formula C₂H₆O, I would recall that in organic compounds there are always methyl groups, CH₃-. Since there are two carbon atoms and six hydrogen atoms I can make two methyl groups,

CH₃- and CH₃- or and

So now I have two methyl groups and one oxygen atom.

and and

The oxygen atom wants to form two bonds (it has two unpaired electrons) and each methyl group wants to form one bond (it has one unpaired electron).

So we just bring the two methyl groups in on either side of the oxygen atom and form the bonds.

We can also represent this structure as,

If we write this structure using condensed formula it would look like, CH₃OCH₃.

The oxygen atom in this structure is bonded to two carbon atoms. When oxygen is bonded to two carbon atoms the compound type is called an ether. We say the R-O-R arrangement is an ether functional group. Here R- is the abbreviation for an organic group with an available carbon bond.

Well that is one structure...what is the other??? The other structure must use the same atoms, but the arrangement of the atoms is different. How could we change the arrangement? In this arrangement we have the oxygen atom between the two carbon atoms. The other arrangement we will move the oxygen between a carbon and a hydrogen atom. So it would look like,

It does not make any difference which carbon and hydrogen we choose they are all the same. This is a different arrangement of the same atoms. In this case the oxygen atom is bonded to one carbon atom and one hydrogen atom. This compound is called an alcohol. We say the R-O-H arrangement is an alcohol functional group. If we write this as a condensed formula is looks like C₂H₅OH or CH₃CH₂OH.

We now know two important functional groups, ether and alcohol.

OK, I'd like to practice finding these two functional groups in some compounds.