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Definition of atomic bonding

It is useful to classify the bonds that hold atoms to one another in chemical compounds and crystals into three types - ionic, covalent and metallic.

As the name implies, ionic bonding is due to the attractions between positively and negatively charged ions. Some atoms are not able to retain all their electrons in competition with other electron greedy atoms.

Under these conditions they lose a few electrons forming cations, ions with a positive charge; the electron greedy atoms gain electrons to become anions, ions with a negative charge.

Oppositely charged ions attract one another forming ionic bonds. The optimum arrangement is one which surrounds each charged ion with several charged ions with the opposite charge.

When the different atoms are almost equal competitors for electrons, neither can take an extra away from the other, and so such atoms bond together by sharing electrons. This kind of bonding is called covalent bonding. It holds two partners together in a very precise geometrical arrangement. The two bonded atoms can be thought of as an ellipsoid with nuclei at the two foci.

Discreet covalently bonded atom groups are found in many minerals. These usually have a net negative charge and are called anionic groups or polyatomic ions. An example is the phosphate ion in which four oxygen atoms surround a central phosphorous atom; the whole unit behaves like an anion with a charge of -3.

Many of these groups form the basis for the common mineral classification schemes (Dana, Strunz).

Atoms in
metals bind together by electron sharing, but in these compounds the electrons are shared between large numbers of atoms and are essentially free to move from atom to atom throughout the material. This type of bonding is weaker. Shear forces can cause the atoms to slip with respect to one another and then re-bond in the new position. This explains the malleability of many metals. The relatively free flow of electrons explains the electrical and heat conductivity of metals.
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