Doric order proportions. It is suggested that these proportions give the Doric columns a masculine appearance, whereas the more slender Ionic columns appear to represent a more feminine look. This sense of masculinity and femininity was often used to determine which type of column would be used for a particular structure. The most influential, and perhaps the earliest, use of the Doric in Renaissance architecture was in the circular "Tempietto" by Donato Bramante (1502 or later), in the courtyard of San Pietro in Montorio, Rome. Before Greek Revival architecture grew, initially in England, in the 18th century, the Greek or elaborated Roman
Ionic bonding cannot exist, as the proximity of the entities involved in the bonding allows some degree of sharing electron density between them. Therefore, all ionic bonding has some covalent character. Thus, bonding is considered ionic where the ionic character is greater than the covalent character. The larger the difference in electronegativity between the two types of atoms involved in the bonding, the more ionic (polar) it is. Bonds with partially ionic and partially covalent character are called polar covalent bonds. For example, Na–Cl and Mg–O interactions have a few percent covalency, while Si–O bonds are usually ~50% ionic and ~50% covalent.