2.2 The Condensed Formula

To illustrate some of the ways we can represent molecular formulae, I will use the example of ethyl alcohol, or C₂H₆O. There are two compounds with this formula, two possible ways to arrange these nine atoms into one molecule that satisfies every single atom. If we write C₂H₅OH, then we're specifying that one of the hydrogens is bonded to the oxygen, narrowing down the structure. From this formula, we can be sure that the compound is none other than ethyl alcohol.

For more complex molecules, there may be a great many ways to arrange their atoms, so this method still won't do. Instead, we can expand the formula out further and write CH₃CH₂OH. This is the condensed formula for ethyl alcohol. Now we are specifying that one of the carbon atoms has three hydrogens, the next one has two, and lastly comes the oxygen atom with its hydrogen. Single bonds are implied, so CH₃CH₂OH is the same as
CH₃-CH₂-OH. Therefore we know that the first carbon is single-bonded to the second carbon, which also shares a single bond with the oxygen.

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