A structure consisting of two or more atoms also has vibrational energy, where the individual atoms move with respect to one another. A diatomic molecule has one molecular vibration mode: the two atoms oscillate back and forth with the chemical bond between them acting as a spring. A molecule with N atoms has more complicated modes of molecular vibration, with 3 N − 5 vibrational modes for a linear molecule and 3 N − 6 modes for a nonlinear molecule. As specific examples, the linear CO 2 molecule has 4 modes of oscillation, and the nonlinear water molecule has 3 modes of oscillation Each vibrational mode has two energy terms: the kinetic energy of the moving atoms and the potential energy of the spring-like chemical bond(s). Therefore, the number of vibrational energy terms is 2(3 N − 5) modes for a linear molecule and is 2(3 N − 6) modes for a nonlinear molecule.