A probability distribution for polymer chain end-to-end separation is derived that incorporates the effects of bond stretching and bending. Each bond is represented by a spring with an equilibrium length that can stretch and contract according to a harmonic force law. Such a model is expected to be important for the description of polymeric materials under large deformations. Methods for computing the distribution and related quantities are derived and are shown to be robust and realistic. Computed distributions show noticeable differences from more commonly used models that do not have a dependence on the bond strengths.