The electron density in the Na-SiOSi plane as a function of R(NaO).
The goal is to illustrate how the electron density of a SiOSi group changes as
a sodium atom bonds to the bridging O atom.
The image shows that, as the Na atom moves towards the O atom, electrons
from O that were in the SiO bond move to the NaO bond. This weakens the SiO bond and thus it
lengthens. Furthermore, the decrease in electron density in the
SiO bond region causes those regions to decrease in repulsion to each other
and so the SiOSi angle thus decreases.
The calculation to make these maps were done with the Gaussian quantum computer program
on a Na(OH2)5 - H6Si2O7 group.