Here is a problem from a physics text An electron (mass 9.11 × 10−31 kg) orbits a hydrogen nucleus at a radius of 5.3 × 10−11 m at a speed of 2.2 × 106 m/s. Find the centripetal force acting on the electron. What type of force supplies the centripetal force? I'm not interested in the answer, rather I thought that electrons didn't orbit in a Newtonian, viz, predictable fashion. I thought they sort of flew around in their orbits in a manner that only vaguely resembles planetary motion.