Multi-configuration Hartree-Fock calculations are reported to study the term splitting in the 1s22s22p2 configuration from Z = 7·0 to Z = 15·0. The wave functions include the Hartree-Fock configuration 1s22s22p2, the 'quasi-degenerate' configuration 1s22p4, the single replacement configurations 1s22s3d2p2 and 1s 22s22p4f, the double replacement configurations from the 2p shell 1s22s23l3l′ (l, l′ = 0, 1, 2) and, finally, the intershell configuration 1s22s3s2p3p. The separations of the 3P, 1D and 1S levels predicted from these functions are in very good agreement with experiment not only for the ratio (3P-1D)/(1D-1S) but also for the individual transitions. These functions have also been studied from Z = 6·0 to Z = 30·0 to compute the contribution to the correlation energy which arises from each configuration. For the 3P and 1D states the 1s22s3d2p2 configurations make a larger contribution to the correlation energy than does the 1s 22p4 configuration at low Z. At higher Z the reverse is true. For the 1S state all the configurations except the 1s 22p4 configuration make a small contribution to the correlation energy throughout the isoelectronic series.