The carboxyl group occurs on the end or side of a molecule. The group consists of a carbon atom that forms two chemical bonds to one oxygen atom and one chemical bond to a second oxygen atom. This second oxygen is also bonded to a hydrogen atom. The arrangement is written -COOH or -C(O)OH (which emphasizes the different chemical bonding between the carbon atom and one of the oxygen atoms). The name "carboxyl" is actually a combination of the words "carbonyl" and" hydroxyl," because the carboxyl group itself can be considered as a combination of carbonyl (CO) and hydroxyl (OH) groups.