Definition Carbohydrates are Carbohydrate: hydrated carbon, carbon plus water polyhydroxy aldehydes and CH ketones which have chemical formulae which or resemble hydrated carbons hence the ChO) name carbohydrate. All of the common sugars found in a better definition: living systems contain either a Polyhydroxy aldehydes or ketones free aldehyde or ketoneCarbohydrates are polyhydroxy aldehydes and ketones which have chemical formulae which resemble hydrated carbons, hence the name carbohydrate. All of the common sugars found in living systems contain either a free or potentially free aldehyde or ketone