Question

How do aldehyde and ketone structures differ?

Answer 1

They both have a oxygen atom double-bonded to a carbon.

Explanation:

The difference is that in a ketone (suffix -one) the `O=` is bonded to a `C` with two other `C`'s attached. In the aldehyde (suffix -al) the `C` is at the end of the chain, so there is also a `H` attached to it.

This combination of `O` and `H` on the same `C` makes it possible for the aldehyde group to oxidize into a `-COOH` (acid) group, while the ketone group cannot.
propanal
propanone
(pictures from wikipedia)