Figure 2-12 The Bohr Model of the Hydrogen Atom In this model, an electron circles the hydrogen nucleus (a proton) only in allowed orbits n = 1, 2, 3, and so forth. The first four Bohr orbits are shown here. This figure is not drawn to scale; in the Bohr model, the n = 2, 3, and 4 orbits are respectively 4, 9, and 16 times larger than the n = 1 orbit.