Entablature being called petrification. The structure of the entablature varies with the three classical orders: Doric, Ionic, and Corinthian. In each, the proportions of the subdivisions (architrave, frieze, cornice) are defined by the proportions of the column in the order. In Roman and Renaissance interpretations, it is usually approximately a quarter of the height of the column. Variants of entablature that do not fit these models are usually derived from them. Pure classical Doric entablature is simple. The architrave, the lowest band, is split, from bottom to top, into the guttae, the regulae, and the taenia. The frieze is dominated by
Ionic compound by a specific equilibrium distance. If the electronic structure of the two interacting bodies is affected by the presence of one another, covalent interactions (non-ionic) also contribute to the overall energy of the compound formed. Ionic compounds are rarely purely ionic, i.e. held together only by electrostatic forces. The bonds between even the most electronegative/electropositive pairs such as those in caesium fluoride exhibit a small degree of covalency. Conversely, covalent bonds between unlike atoms often exhibit some charge separation and can be considered to have a partial ionic character. The circumstances under which a compound will have ionic or covalent