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The bond valence model [1] is an exact representation of the ionic model. It gives a good empirical description of all types of polar bond, regardless of ionicity or covalency. Unlike Atoms in Molecules (AIM) [2] where the property of an atom depends on its context, the atoms in the ionic model are invariant soft charged spheres bound together in a crystal by electrostatic forces. Each cation is linked (bonded) to its neighbouring anions by electrostatic flux (lines of field) that sum around each atom to the atomic charge. The magnitude of the flux is known as the bond valence. The structure of a solid can thus be represented by a network in which the nodes (atoms) are linked by bonds. However, just as the atoms of the bond valence model are not the same as the atoms in AIM, so the bonds in this model are not the same as the bond paths in AIM. Atomic charges in the ionic model may be assigned any value provided that the charge on a given atomic species is always the same, that the cations are positive, the anions negative, and the whole array is electroneutral. However, it is conventional for the charges to be chosen equal to the number of valence electrons used in bonding as this results in the bond valence being the same as the number of electron pairs associated with the bond. To prevent the array of charges from collapsing to a point it is necessary to introduce a repulsive force between the atoms, conveniently represented by an inverse exponential with two empirically fitted parameters, relating the bond valence to the bond length. The bond network can be represented by a graph making the model conceptually and computationally simple. Bond valences can be predicted by ensuring the sum of bond valences around any loop in the graph is zero. It is thus possible to predict the ideal bond lengths in any compound from the bond graph without knowledge of the 3-dimensional structure; indeed in high symmetry cases the 3-dimensional structure can be predicted directly from

Bond strengths, a crucial question for the chemist. Insight on the oxoanions containing iodine(V)