Electron configuration of a bonded atom

[Metabolics]

Hi everyone,

I was wondering if the electron configuration of an atom changes when it is bonded to other atoms.

For instance, O is [He]2s^2 2p^4. If O is bonded to two hydrogens, does this increase the electron configuration to [Ne]?

The reason I ask this is because sulfur's electron configuration is [Ne]3s^2 3s^4. It has access to the 3d orbital (because sulfur n=3, and the 3d orbital, while it is in a different period, has n=3 as well), which apparently explains why it can bond to many more atoms. When these bonds occur, does the electron configuration of sulfur change, as in do electrons "add" to the d orbital? Can you predict the maximum number of bonds it can make based off of the space in the d orbital? Does the 4s orbital fill as atoms are bonded to S, or does the 3d fill?

Some people have told me that the 4s fills first, but then my reasoning as to why S can utilize the 3d orbital is flawed (since they are both n=3).

Thanks ahead of time.

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[Dasypus]

In essence, your questions are why molecular bonding theory was developed! The outer electrons of a bonded atom aren't 'pure' any more, but rather hybridize with those of the other participants in the bond. You're right that S can expand its octet because it has access to the 3d orbital, but it's not that those subshells fill normally, like they would to form an anion. Rather, they are available to hybridize with the valence shells of the other bonded atoms.