Each mole of CaO introduces one mole of oxygen ions in the hexagonal network of silica and can break two vertices of the hexagonal structure of silica. By adding 2 moles of  for every mole of silica all the four vertices are broken and we simply have  and  as shown below

Note that  can combine with two tetrahedrons

The reaction between alkaline base oxides, e.g. Na₂O and SiO₂ is as follows:

and

Since Na has one charge, each tetrahedron of silica will have Na ion attached to oxygen ion. As a result one should expect more decrease in viscosity of silica on addition of alkaline base oxides as compared with basic oxides.