Regarding molten slags used for iron and steel making, discrete anion models, SiO₄^4- and Si₂O₇^6-, coordinating metal irons such as Na⁺, K⁺, Ca²⁺ and Mg²⁺ were examined by the DV-Xα method. The bond order which is a measure of the covalent bond and the ionicity which is a measure of the charge transfer were calculated. The bond orders between the Si ions and the uni-bonding oxygen ions were found to be very high. On the other hand, the bond orders between the Si ions and the oxygen ions coordinating the metal ions were very low, that is, the covalent bonds between them are weak, indicating that these oxygen ions appear to become free oxygen ions. The metal ions such as Na⁺, K⁺, Ca²⁺ and Mg²⁺ are necessary for the formation of the free oxygen ions as well as the decomposition of polymerized structures. The values of ionicity of the uni-bonding oxygen ions were -0.5∼-1.2 and those of the oxygen ions coordinating the metal ions were -2.3∼-2.5. These values of oxygen ions are approximately equal to the valences obtained from the statistical thermodynamics studies.