Atom Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and typically a similar number of neutrons. Protons and neutrons are called nucleons. More than 99.94% of an atom's mass is in the nucleus. The protons have a positive electric charge, the electrons have a negative electric charge, and the neutrons have no electric charge. If the number of protons and electrons are equal, that atom is electrically neutral. If an atom has more or fewer electrons than protons, then it has an overall negative
Vector model of the atom The process of adding all angular momenta together is a laborious task, since the resultant momenta is not definite, the entire cones of precessing momenta about the z-axis must be incorporated into the calculation. This can be simplified by some developed approximations - such as the "Russell-Saunders coupling" scheme in L-S coupling, named after H. N. Russell and F. A. Saunders (1925). Vector model of the atom In physics, in particular quantum mechanics, the vector model of the atom is a model of the atom in terms of angular momentum. It can be considered as the extension of the Rutherford-Bohr-Sommerfeld