text: A chemical structure can be represented by a bond network of the kind familiar in molecular diagrams.  The infinitely connected bond networks found in crystals can be simplified into finite networks by extracting one formula unit and reconnecting any broken bonds to each other.  If the bond network is not known, a plausible network can be created by connecting well matched cations and anions that satisfy Eq. 4.  If the finite network contains only cation-anion bonds, every bond can be treated as an electric capacitor (two equal and opposite charges linked by electrostatic flux).  The bond network is thus equivalent to a capacitive electrical circuit with the charge on each capacitor being equivalent to the bond valence.  The individual bond capacitors are not initially known, but in the absence of any information to the contrary we assume that they are all equal.  In this case the circuit can be solved using the Kirchhoff equations, yielding the valences of each bond.  Eq. 2 can then be used to calculate bond lengths which are found to lie within a few picometres of the observed bond lengths if no additional constraints are present.  Additional constraints include electronic anisotropies (lone pairs and Jahn-Teller distortions) or steric constraints, (bonds stretched or compressed in order to fit them into three-dimensional space).  Hydrogen bonds are an example of a steric constraint. The repulsion resulting from the close approach of the donor and acceptor atoms causes the bonds to be stretched, and under this constraint the distortion theorem predicts that the hydrogen atom will move off-center.
  The bond valence is a vector directed along the bond since it represents the electrostatic field linking the ions.  If the atom is unconstrained, the sum of the bond valence vectors around an atom is expected to be zero, a condition that limits the range of possible bond angles.