The hydrogen atom (H) simultaneously interacts with two or more other atoms, outwardly expressed by the fact that the distance between these atoms is smaller than the sum of the respective so-called atomic radii. Because the ability to form a H-bridge is based on fine-constitutive properties of hydrogen (for example coordinative "forces", which may also be expressed by saying that the configurative -- not the electronic -- valence of H is greater than 1 (but therefore not necessarily equal to 2)), its intensity neither may be expressed classically electrostatically, nor in this way be treated mathematically theoretically, but only on the basis of quantum mechanics. This is just another reason why the hydrogen bond often is underestimated as to its significance and power.