Hypothetically, if you had a gas made of really heavy atoms/molecules (although it's unlikely that they would be stable at the kind of Uranium-heavy I'm thinking of, let's say that hypothetically they are) in a liquid made of really really light molecules or atoms (e.g hydrogen), and say that temperature isn't going to change the given states of the elements (very very hypothetically), and so they can exist in the states they need to together, could the bubbles go down? Or would the relative densities make the masses of the atoms and molecules irrelevant? 

I know the air inside the lungs makes people float and just like that,the air inside a ship decreases the density of the total volume and hence makes the ship float.But what happens if you vacuum the air inside the ship and then seal it somehow,just like exhaling air from your lungs,does the ship sink cause the density of the total volume will just be the density of them metals inside the ship despite the airless big space in it?