An electric field distorts the charge distribution of an atom. For states, the energy is decreased by to second order in the field strength. The parameter is known as the (electric) polarizability. We consider the and states of the hydrogen atom, making use of perturbation theory. The graphic shows a contour plot of the wavefunction as the electric field is increased. The wavefunction is positive in the blue region and negative in the yellow region. A similar distortion of the initially spherical charge density occurs in the formation of chemical bonds.