Aldehydes and ketones are carbonyl compounds because they contain the C=O group. In aldehydes the C=O is at the end of the chain (-CHO), and in ketones it is inside the chain.Oxygen is more electronegative than carbon, so the C=O bond is polar, with Cδ+ and Oδ-. The double bond is made of one σ bond and one π bond, and the atoms around the carbonyl carbon are trigonal planar at 120°.The δ+ carbon is attacked by nucleophiles such as the hydride ion and the cyanide ion. Carbonyl compounds therefore undergo nucleophilic addition, unlike the electrophilic addition of alkenes.Short-chain aldehydes and ketones dissolve in water because the oxygen lone pairs form hydrogen bonds with water molecules.