The concept was developed in the middle of the nineteenth century in an attempt to rationalize the formulae of different chemical compounds. In 1919, Irving Langmuir, borrowed the term to explain Gilbert N. Lewis's cubical atom model by stating that "the number of pairs of electrons which any given atom shares with the adjacent atoms is called the covalence of that atom."  The prefix co-, e.g. co-author, means together, jointly, associated in action, partnered to a lesser degree,  etc.,; thus a co-valent bond, essentially, means that the atoms share<unk>   Hence, if an atom, for example, had a +1<unk>  meaning it was missing an electron, and another a -1<unk>  meaning it had an extra electron, then a bond between these two atoms would result because they would be complementing or sharing their out of balance<unk> tendencies. Subsequently, it is now more common to speak of covalent bonds rather than<unk> ", which has fallen out of use in higher level work with the advances in the theory of chemical bonding, but is still widely used in elementary studies where it provides a heuristic introduction to the subject.
Valence 
Providencia
Cognitivism 
Impaction
Avolition
Impalement
Anise
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