electron shell同electron shell中間有d咩

I think you should ask your physics teacher...

I can tell you between electron shells there are space. However it is wrong to get pictures like this. you treat everything in a classical way.
i.e. you think of the 3D world.

In fact, there are quantum theory explaining it. it is related to energy.
quantum theory has nothing to do with space and 3D world, and
sometimes appear contradictory to classical theory