A carbocation is an ion with a positively-charged carbon atom. The charged carbon atom in a carbocation is a "sextet" (that is, it has only six electrons in its outer valence shell instead of eight valence electrons.) Carbon atoms with eight valence elections have the maximum stability (octet rule). Therefore, carbocations are often reactive, seeking to fill the octet of valence electrons as well as regain a neutral charge. Logic would say that carbocation have sp hybridization with an empty sp orbital giving positive charge. However, the reactivity of a carbocation more closely resembles sp hybridization with a trigonal planar molecular geometry.