So I thought of a nice question: how close-in does the hydrogen in Rubidium Hydride sit. For gaseous RbH and thinking in solid spheres instead of clouds:

  The bond length of RbH is ~4.5 units.

  The Hydrogen proton is *inside* the empty 5s radius (~4.7 units).

  If we added an electron ("an antibonding electron") it would go into the 5s orbital. But that stretches the bond making the distance between the nuclei ~4.8 units.

  In RbH, the Rb atom gives up its single outer 5s electron to the H atom, so there is no populated 5s electron shell in a Rubidium Hydride molecule.