Observe a spoked wheel on an overturned bicycle. Note that it is made up mostly of space.

The spokes could represent electrons that spin rapidly around the center or nucleus of an atom.

Set a ping-pong ball behind the wheel to represent the nucleus. Now turn the wheel and try to throw beans or wads of paper through the spokes. Even though the spokes occupy only a small fraction of the space within the wheel, due to their rapid movement, they stop the beans from passing through.

In a similar way, electrons in an atom move and occupy the space surrounding the nucleus.