Naming functional groups

[204623782]

When it's presented as CH3CH2CHO, like just written out like that, I have a hard time identifying the functional group. Is there an easy way to tell, or does it just come with practice?

[Rex Lee 1C]

What's important in this structural formula is the ending -CHO. This implies that there is an oxygen and hydrogen attached to a carbon which is attached to the rest of the chain. However, since this is only 3 bonds and to get carbon a formal charge of zero, we double bond the oxygen. Now it is clear that this is an aldehyde group, the compound being propanal.