How can a study feel out the shape of an atom? Atoms are made of two main parts, and each part necessitates a different method. In the very center of the atom is the tiny nucleus, a dense cluster of protons and neutrons. The space surrounding this nuclear core is a group of electrons, known as the electron cloud. The latter dwarfs the former: if the nucleus were magnified to the size of a marble, the electron cloud would extend roughly a quarter of a mile in all directions from it.