Lewis Theory An Overview

Electrons, especially those of the outermost (valence) electronic shell, play a fundamental role in chemical bonding. 

In some cases, electrons are transferred from one atom to another. Positive and negative ions are formed and attract each other through electrostatic forces called ionic bonds. 

In other cases, one or more pairs of electrons are shared between atoms. A bond formed by the sharing of electrons between atoms is called a covalent bond. 

Electrons are transferred or shared in such a way that each atom acquires an especially stable electron configuration. Usually this is a noble gas configuration, one with eight outer-shell electrons, or an octet. 

Lewis developed a special set of symbols for his theory. A Lewis symbol consists of a chemical symbol to represent the nucleus and core (inner-shell) electrons of an atom, together with dots placed around the symbol to represent the valence (outer-shell) electrons. Thus, the Lewis symbol for silicon, which has the electron configuration [Ne]3s 3p, is 

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Lewis Theory An Overview—Lewis symbol represents the valence electrons of an atom by using dots placed around the chemical symbol. A Lewis structure is a combination of Lewis symbols used to represent chemical bonding. Normally, all the electrons in a Lewis structure are paired, and each atom in the structure acquires an octet—that is, there are eight electrons in the valence shell. In Lewis theory, chemical bonds are classified as ionic bonds, which are formed by electron transfer between atoms, or covalent bonds, which are formed by electrons shared between atoms. Most bonds, however, have partial ionic and partial covalent characteristics. 

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