A carbocation was previously often called a "carbonium ion" but chemists question the exact meaning. In present-day chemistry, a carbocation is any positively charged carbon atom. Two special types have been suggested: carbenium ions are trivalent and carbonium ions are pentavalent or hexavalent. University level textbooks only discuss carbocations as if they are carbenium ions, or discuss carbocations with a fleeting reference to the older phrase of carbonium ion or carbenium and carbonium ions. One textbook to this day stays with the older name of carbonium ion for carbenium ion and reserves the phrase "hypervalent carbenium ion" for CH.