H2O
 

When the compound of H2O is broken down, Is the atomic volume for the three atoms still the same?

Good question. In water, some of the electrons are in the bonds between atoms, and so the shape of the molecule is different than the shape of the individual atoms or molecules (O2 and H2). I'd guess that the volume is different, but I'm not sure. It's an oddly worded question.

I have tested breaking down h2o in a pop bottle, and yes, The volume can/will increase to the point of the bottle bursting open.

Oh, that is a different situation, TS, than what I thought you meant. You are describing breaking down H2O molecules into O2 and H2 and the volume of the resulting gas assuming constant pressure. Even if the H2O molecules started out gaseous, two H2O gas molecules will make two H2 gas molecules and an O2 molecule. The number of moles of gas in the container increases, and by the Ideal Gas Law you can see that the pressure and/or volume will increase.

When you wrote "atomic volume" I thought you mean the volume of the atoms, not the volume of the gas.

Cool! I never realized that happened. :!: :D