<P> A chemical bond is an attraction between atoms . This attraction may be seen as the result of different behaviors of the outermost or valence electrons of atoms . These behaviors merge into each other seamlessly in various circumstances, so that there is no clear line to be drawn between them . However it remains useful and customary to differentiate between different types of bond, which result in different properties of condensed matter . </P> <P> In the simplest view of a covalent bond, one or more electrons (often a pair of electrons) are drawn into the space between the two atomic nuclei . Energy is released by bond formation . This is not as a reduction in potential energy, because the attraction of the two electrons to the two protons is offset by the electron - electron and proton - proton repulsions . Instead, the release of energy (and hence stability of the bond) arises from the reduction in kinetic energy due to the electrons being in a more spatially distributed (i.e. longer de Broglie wavelength) orbital compared with each electron being confined closer to its respective nucleus . These bonds exist between two particular identifiable atoms and have a direction in space, allowing them to be shown as single connecting lines between atoms in drawings, or modeled as sticks between spheres in models . </P> <P> In a polar covalent bond, one or more electrons are unequally shared between two nuclei . Covalent bonds often result in the formation of small collections of better - connected atoms called molecules, which in solids and liquids are bound to other molecules by forces that are often much weaker than the covalent bonds that hold the molecules internally together . Such weak intermolecular bonds give organic molecular substances, such as waxes and oils, their soft bulk character, and their low melting points (in liquids, molecules must cease most structured or oriented contact with each other). When covalent bonds link long chains of atoms in large molecules, however (as in polymers such as nylon), or when covalent bonds extend in networks through solids that are not composed of discrete molecules (such as diamond or quartz or the silicate minerals in many types of rock) then the structures that result may be both strong and tough, at least in the direction oriented correctly with networks of covalent bonds . Also, the melting points of such covalent polymers and networks increase greatly . </P> <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>

What is the cause of chemical bonding of atoms of elements