Formal charge on oxygen

The formal charge on oxygen in 1-10 is —1. There are six unshared electrons and 2/2 = 1 electron from the pair being shared. Thus, the number of electrons is seven, which is one more than the number of valence electrons for oxygen. 

The structural framework of silica [5] is based on interconnected Si(-0->4 tetrahedra, with some OH terminations at the surface. Aluminas are built primarily of A1(-0-)4 tetrahedra and AK-O-) octahedra, with some surface-OH terminations [6]. The fundamental framework structure of aluminosilicates include primarily Si(-0-)4 and AK-O-) units plus charge compensating bridging or framework hydroxyl groups, namely structure I, which shows formal charges on oxygen and aluminum [7]. On the basis of these kinds of structures and various so-called defect structures that may include octahedral and three-coordinate aluminum sites, the investigation by NMR of a wide variety of nuclei can be anticipated. Numerous NMR studies based on Si, Al, H, H, and O have been reported on silica, alumina, and silica-alumina systems. 

Give the formal charge on oxygen in each compound, (a) CH3—O—CH3... 

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