Lewis Structures

As mentioned above, the shared valence electrons of a covalent bond are called the bonding
electrons, while the valence electrons not involved in the covalent bond are called nonbonding
electrons, also called lone electron pairs. A convenient notation, called a Lewis structure (examples
of which have already been shown), is used to represent the bonding and nonbonding electrons in a
molecule, facilitating chemical “bookkeeping.”

The number of valence electrons attributed to a particular atom in the Lewis structure of a molecule
is not necessarily the same as the number would be in the isolated atom, and the difference
accounts for what is referred to as the formal charge of that atom. Often, more than one Lewis
structure can be drawn for a molecule; this phenomenon is called resonance.

DRAWING LEWIS STRUCTURES

A Lewis structure, or Lewis dot symbol, is the chemical symbol of an element surrounded by dots,
each representing one of the s and/or p valence electrons of the atom. The Lewis symbols of the
elements found in the second period of the periodic table are shown below.

Just as a Lewis symbol is used to represent the distribution of valence electrons in an atom, it can
also be used to represent the distribution of valence electrons in a molecule.