Final answer:
An aldehyde and a ketone with the same molecular formula have different structures; propanal (CH3CH2CHO) and acetone (CH3COCH3) are examples for C3H6O. Aldehydes end with an '-al' suffix while ketones end with '-one'.
Step-by-step explanation:
An aldehyde and a ketone can indeed have the same molecular formula but different structures due to the placement of their carbonyl group. An aldehyde has a carbonyl group attached to at least one hydrogen atom, whereas a ketone has its carbonyl group positioned between two carbon atoms.
Consider the molecular formula C3H6O. The aldehyde with this formula is propanal, with the structure CH3CH2CHO, whereas the ketone is acetone, with the structure CH3COCH3.
In naming these compounds, the suffix for aldehydes is -al, and for ketones is -one. Propanal is named by identifying the longest carbon chain with the aldehyde group (propane) and replacing -e with -al. Acetone is similarly named by finding the longest carbon chain containing the carbonyl (propanone) and replacing -e with -one.