nucleus: the massive, positively charged central part of an atom, made up of protons and neutrons. J. J. Thomson, who discovered the electron in 1897, proposed the plum pudding model of the atom in 1904 before the discovery of the atomic nucleus in order to include the electron in the atomic model. read more
Thomson proposed a 'plum pudding' model, with positive and negative charge filling a sphere only one ten billionth of a metre across. Maybe he came up with it, maybe it was his wife. There is no record either way, but it was Thompson himself that first used the term. read more
Based on it’s appearance, which consisted of a “sea of uniform positive charge” with electrons distributed throughout, Thompson’s model came to be nicknamed the “Plum Pudding Model”. Though defunct by modern standards, the Plum Pudding Model represents an important step in the development of atomic theory. read more
First proposed by J. J. Thomson in 1904 soon after the discovery of the electron, but before the discovery of the atomic nucleus, the model represented an attempt to consolidate the known properties of atoms at the time: 1) electrons are negatively-charged particles and 2) atoms are neutrally-charged. read more