Network solid and Empirical formula question

[Ultimeaciax]

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In Silica, its empirical formula is SiO2. Looking at that, it's a 1:2 ratio. Thus, I guess there would be 2 O's for every 1 Si. However, its molecular formula is SiO4. How can this be? For future q's, how can I determine the molecular formula given something this tricky?

 

[nuD]

Crystalline silica has an Si:O ratio of 1:2 so it's molecular formula is SiO2 like the empirical formula. It's just that each Si is surrounded by 4 O's -- this is possible while still maintaining the 1:2 ratio because each O is bonded to more than one Si.

From what I've seen, if empirical/molecular formula questions show up on the MCAT, they will more likely be in the form of calculating a molecular formula of an organic molecule based on an experiment, or converting between molecular and empirical formulas for organic molecules.