1 Jan 1913 Jahr - 1913 Niels Bohr Bohr discovered atomic orbitals. He proposed that electrons travelling around the nucleus could only occupy orbits that had fixed energy values, being multiples of n, where n represents the energy level. Each value of n is associated with an orbit of different radius. Bohr accurately predicted the line spectrum of the hydrogen atom. This work led to the planetary model of the atom, in which electrons circle the atom's nucleus in fixed circular paths as the planets do around the Sun. (Band der Zeit)