PH₃ and compounds derived from it by substituting one, two or three hydrogen atoms by hydrocarbyl groups R₃P. RPH₂, R₂PH and R₃P (R ≠ H) are called primary, secondary and tertiary phosphines, respectively. A specific phosphine is preferably named as a substituted phosphane, e.g. CH₃PH₂ methylphosphane.