English: This is a diagram of an atom with seven electrons, as described J. J. Thomson in a lecture in 1905. In that lecture, he presented a diagram (File:Thomson_atom_electron_arrangements.jpg) in which he showed hypothetical arrangements of electrons in an atom. This image is based on Thomson's rendition of a seven-electron atom. The electrons are arranged in a pentagonal dipyramid. At the time, Thomson believed that even small atoms contained thousands of electrons, but calculating how so many electrons would arrange themselves in an atom was too computationally difficult for him. In 1913, scientists deduced that an atom contains a number of electrons equal to its atomic number. This atom with seven electrons would therefore be nitrogen, but by then the plum pudding model had been declared obsolete.