Here, J is the total electronic angular momentum, L is the orbital angular momentum, and S is the spin angular momentum. Because S = 1 / 2 for electrons, one often sees this formula written with 3/4 in place of S ( S + 1 ) . The quantities g L and g S are other g -factors of an electron. For an S = 0 atom, g J = 1 and for an L = 0 atom, g J = 2 .