Helium atom. Illustration of the atomic structure and electron configuration of the element helium. An atom of this element has 2 electrons (blue) shown here in orbit round the nucleus (centre). The two electrons are in the first shell (the 1s orbital). The isotope shown here is helium-4, with a nucleus of 2 protons (red) and 2 neutrons (grey). All isotopes of an element have the same electronic structure.