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Chemical Compounds

  Chemical elements are usually never found in a pure state, but are generally combined with other elements and mixed with many others. The elements are linked together by means of chemical bonds. This bonding is haphazard but corresponds to the atomic structure of each element.

The ability of any atom to combine is determined by the number of electrons that occur in the atom\'s outer shell. If this outer shell is not full, the atom will try to attach itself to another atom in order to become stable. The ‘inert gases’ such as neon and krypton are stable since their outer shell has a full complement of eight electrons, not allowing interaction with other elements.

Since eight electrons give stability and a lack of structure with which to combine, the atoms with seven electrons will try to ‘borrow’ an electron from an atom which has one more than eight. Both atoms become stable as the electron from one has been ‘borrowed’ by the other, and so both now have eight electrons in their outer orbits. Two such atoms are sodium, which has only one electrons in its outer shell, and fluorine which has seven; these readily combine to form a stable compound, sodium fluoride, where the two elements in the process of borrowing and giving now have the full quota of electrons in their respective outer shells.

Hydrogen atoms have one electron orbiting the nucleus and do not occur singly (except as short-lived intermediates during some chemical reactions or at high temperatures), but consist of molecules each having two hydrogen atoms joined together. This means that the molecule has now two electrons in the shared outer shell.

Since electrons carry a negative charge, an atom with too many electrons becomes a negative ion and too few a positive ion. Positive and negative ions combine in compounds to cancel each other out, so giving overall neutrality. Not all atoms ionize to form compounds but some, especially organic compounds, share electrons in covalent bonds and remain electrically neutral. AA

See also chemistry.Further reading H.B. Gray, Chemical Bonds.



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