A structural model is presented for binary silicate systems of the typeMO-SiO2, whereMO is a basic oxide, in which silicate tetrahedra and oxygen “bridges” are treated as structural units. One single formalism applies over the entire composition range from pureMO, where the model reduces to a simple orthosilicate anion model, to pure SiO2, where the model reduces to a simple model of the breaking of oxygen “bridges” upon the addition ofMO. At intermediate compositions, chain length distributions for silicate polymer chains can be calculated from the model, even though these polymeric chains are not explicitly treated as structural units of the model. The calculated chain length distributions are in very good agreement with those calculated from the polymeric model of Masson for all systems studied. Furthermore, two dimensional (cyclic) and three dimensional (network) polymeric structures are accounted for by the present model. The model accounts well for available enthalpy, entropy, activity, and phase diagram data in the binary liquid systemsMO-SiO2 whereM = Ca, Mg, Mn, Fe, or Pb. The observed variations of ΔH with composition and from system to system are explained in terms of the energies of the various bonds and are represented by a three parameter equation. Although the model has been tested here only for liquid slags, it should be useful in understanding the structure of silicate glasses as well.