Ab initio density functional theory calculations are performed to anal
yze a regional reactivity index based on chemical concepts of local so
ftness and electronegativity. This leads to the prediction of a genera
l qualitative pattern for the interaction of the Si(111)-(7 x 7) surfa
ce with atoms and molecules that preserve the reconstruction. We succe
ssfully compare this general pattern with experimental information ava
ilable. Based on this approach, we predict the reactivity behavior of
the reconstruction with a wide range of chemical reactants.