We performed a first-principles molecular dynamics study of liquid SiO2 at a temperature of 3500 K, followed by a rapid quench to 300 K obtaining a perfectly chemically ordered amorphous network. Structural and electronic properties of our amorphous sample are in good agreement with neutron diffraction, x-ray photoemission, and optical experiments. On the basis of the partial structure factors, we investigated the origin of the first sharp diffraction peak. Disorder affects differently the localization properties of valence and conduction band states, as suggested by experimental mobilities of electrons and holes.