The model of an atom put forward by Ernest Rutherford in 1911 on the basis of experiments on the scattering of alpha particles. The model consisted of a very dense positively charged nucleus, with electrons orbiting round the nucleus. This model presented a serious difficulty for the classical theory of electricity and magnetism, which predicts that the electron should spiral into the nucleus in a fraction of a second, radiating electromagnetic energy while doing so. This difficulty led to the development of the Bohr theory in 1913 and was definitively solved by the development of quantum mechanics and its application to atomic structure in the mid 1920s.