Bohr's model succeeded for hydrogen but he could not extend it to helium because helium has:

1. Bohr incorporated Planck's quantisation and Einstein's photons into a classical description of the atom. 2. That gave a theoretical expression for the Rydberg constant, a remarkable achievement. 3. Despite it, he was unable to extend his theory to the next simplest atom, helium, which only has two electrons. 4. The difficulty is the interaction between the two electrons, not the nucleus. 5. Multi-electron atoms needed the full quantum mechanical treatment that followed. _Source: OpenStax Chemistry 2e (CC BY 4.0), Ch 6 'Electronic Structure and Periodic Properties of Elements', sections 6.1-6.5_