<P> In a simplified view of an ionic bond, the bonding electron is not shared at all, but transferred . In this type of bond, the outer atomic orbital of one atom has a vacancy which allows the addition of one or more electrons . These newly added electrons potentially occupy a lower energy - state (effectively closer to more nuclear charge) than they experience in a different atom . Thus, one nucleus offers a more tightly bound position to an electron than does another nucleus, with the result that one atom may transfer an electron to the other . This transfer causes one atom to assume a net positive charge, and the other to assume a net negative charge . The bond then results from electrostatic attraction between atoms and the atoms become positive or negatively charged ions . Ionic bonds may be seen as extreme examples of polarization in covalent bonds . Often, such bonds have no particular orientation in space, since they result from equal electrostatic attraction of each ion to all ions around them . Ionic bonds are strong (and thus ionic substances require high temperatures to melt) but also brittle, since the forces between ions are short - range and do not easily bridge cracks and fractures . This type of bond gives rise to the physical characteristics of crystals of classic mineral salts, such as table salt . </P> <P> A less often mentioned type of bonding is metallic bonding . In this type of bonding, each atom in a metal donates one or more electrons to a "sea" of electrons that reside between many metal atoms . In this sea, each electron is free (by virtue of its wave nature) to be associated with a great many atoms at once . The bond results because the metal atoms become somewhat positively charged due to loss of their electrons while the electrons remain attracted to many atoms, without being part of any given atom . Metallic bonding may be seen as an extreme example of delocalization of electrons over a large system of covalent bonds, in which every atom participates . This type of bonding is often very strong (resulting in the tensile strength of metals). However, metallic bonding is more collective in nature than other types, and so they allow metal crystals to more easily deform, because they are composed of atoms attracted to each other, but not in any particularly - oriented ways . This results in the malleability of metals . The cloud of electrons in metallic bonding causes the characteristically good electrical and thermal conductivity of metals, and also their shiny lustre that reflects most frequencies of white light . </P> <P> Early speculations about the nature of the chemical bond, from as early as the 12th century, supposed that certain types of chemical species were joined by a type of chemical affinity . In 1704, Sir Isaac Newton famously outlined his atomic bonding theory, in "Query 31" of his Opticks, whereby atoms attach to each other by some "force". Specifically, after acknowledging the various popular theories in vogue at the time, of how atoms were reasoned to attach to each other, i.e. "hooked atoms", "glued together by rest", or "stuck together by conspiring motions", Newton states that he would rather infer from their cohesion, that "particles attract one another by some force, which in immediate contact is exceedingly strong, at small distances performs the chemical operations, and reaches not far from the particles with any sensible effect ." </P> <P> In 1819, on the heels of the invention of the voltaic pile, Jöns Jakob Berzelius developed a theory of chemical combination stressing the electronegative and electropositive characters of the combining atoms . By the mid 19th century, Edward Frankland, F.A. Kekulé, A.S. Couper, Alexander Butlerov, and Hermann Kolbe, building on the theory of radicals, developed the theory of valency, originally called "combining power", in which compounds were joined owing to an attraction of positive and negative poles . In 1916, chemist Gilbert N. Lewis developed the concept of the electron - pair bond, in which two atoms may share one to six electrons, thus forming the single electron bond, a single bond, a double bond, or a triple bond; in Lewis's own words, "An electron may form a part of the shell of two different atoms and cannot be said to belong to either one exclusively ." </P>

Which of the following is not a way in which chemical bonds can be formed