Chemical bond





In chemistry and allied sciences, a chemical bond is the force which holds
atoms together in molecules or crystals. In simple compounds, concepts such
as valency or oxidation number can help determine whether or not atoms can
bond with other atoms of the same or different type in a certain way. With
more complicated compounds, such as complexes, valence concepts fail and a
more thorough understanding of quantum mechanics is necessary.

The spatial characteristics and range of energies encompassed by chemical
forces span a continuum, making the terms for the different types of
chemical bond somewhat arbitrary or overlapping in their applicability, but
the types include:

   * ionic bond
   * covalent bond
   * coordinate covalent bond
   * metallic bond

In all types of bonding, the electronic configuration of the molecule or
substance (in the case of extended array structures, such as found in
crystals). The types of bonding are differentiated by the extent to which
electron density is localized or delocalized among the atoms of the
substance. In the case of ionic bonding, electrons are more tightly
associated with individual atoms, with net charges being assigned to
discrete constituent atoms throughout the substance, with the nature of the
interatomic (or more appropriately) interionic forces largely characterized
by isotropic continuum electrostatic potentials.

In contrast, the electron density distributions within covalent bonds are
not so readily assigned to individual atoms, but are instead delocalized
across the molecule in structures sometimes described as molecular orbitals,
which may have more directed, anisotropic properties. Intermediate
situations certainly exist, with bonds having some mix of polarized
ionic-like nature and some more electronically dispersed structure.

Ionic bonding can largely be described by classical mechanics, but the
complexity of covalent bonding relies more heavily on concepts from quantum mechanics.

Other attractions between atoms/molecules

Other types of interatomic and intermolecular forces that occur within the
chemical energy regime, but which are not characterized as bonds are:

   * London forces
   * hydrogen bond attraction
   * Intermolecular force