The Greeks already indicated the existence of a fundamental particle, acting being constituents of matter, predicting the existence of a few atoms of small size, and listing a small amount of different types of them. Until the end of the 19th century were not discovered more data on those items. J. j. Thomson, along with other scientists, discovered in 1897 that atoms were indivisible as he was believed, but that could be separated into small components.
He discovered the composition of atoms and the existence of particles that orbiting in the outer zone calls electrons, whose mass was much smaller than the nucleus. The core for its part, had positive charge and its weight was almost the totality of the atom. While he was not able to determine the composition of the nucleus, were sitting the basis for further investigations, the first of which focused on the structure of the atom. The atom consists of a nucleus of great size that orbit the electrons. It was e. Rutherford who developed a model based on a solar system in miniature, in which the nucleus was a star (the Sun) and the electrons in 1911 the planets. The explanation of his theory had two errors: 1 – that the electrons would issued power spin, decreasing its speed would then fall to the nucleus; erroneous because the electrons occupy fixed orbits. The second error was that electrons could jump from one orbit to any other around the nucleus.