Based on the calculation of pair correlation energy contributions of FX (X = OH, NH2, CH3) systems and the comparison of three partition schemes, the total correlation energies of these AB type covalent molecules have been approximated using the simple scaling ionic partition scheme. Incorporating our early works on strong ionic compounds MA and A(2) symmetric molecules, the general formula is summarized to estimate the total correlation energy for different kinds of chemical bonding systems. Comparison of the ratio of scaling coefficients for MA compounds, AB type and A(2) symmetric molecules shows that the ratio depends on the ionic property of the system. (C) 2004 Elsevier B.V. All rights reserved.