Chlorine atom. Diagram of an atom of the element chlorine showing its surrounding electron orbitals. Chlorine is the 17th element, and has 17 protons (red) in its nucleus, along with most commonly 18 neutrons (blue). Chlorine has 17 electrons, and each of its orbitals can hold a maximum of two. Orbitals are filled from the lowest energy (nearest the nucleus) first, so there are two electrons in the inner 1s orbital, and two in the higher energy 2s orbital (green spheres), and two each in the slightly higher energy 2p orbitals (blue, red and yellow). Outside the 2p orbitals is a spherical 3s shell, and three 3p shells. Two of the 3p shells (blue and brown) hold two electrons, while the last (magenta) holds only one. For clarity, solid lines show the paths of the electrons. In reality, electrons can be found anywhere, and the shape of each orbital is based only on where it is most likely to be found.