So an aldehyde is when the C in the carbonyl group is connected to a CH3 group and an H? (H and C or two H are bonded with the carbonyl. - GS). And a ketone is when that H is something else right? (Two carbons are bonded with the carbonyl. - GS). So the difference (in structure) between them would be just that one “R” group? (Presence of H makes the difference. - GS).