Covalent Bonds

Covalent bonds result from the sharing of  valence electrons, thus the term “covalent”. Since the octet rule is still observed for most covalent compounds, elements obtain a noble gas configuration by sharing, rather than by transferring, electrons. (Remember that H follows a “duet rule”.)

A single covalent bond requires 2 electrons, which is indicated by a line between the atoms. To construct a Lewis representation for covalent compounds, we must first determine an arrangement of the component atoms; this is commonly referred to as a skeleton structure. In many cases, more there one structure will work in forming a reasonable Lewis dot diagram, so other evidence may be needed to determine the correct arrangement.

H2O

Sulfur dioxide actually has a sulfur atom between the two oxygens, but a central oxygen also yields a proper Lewis dot structure. Therefore, the first step in building a skeleton structure is to determine the central atom. This information can, at times, be problematic requiring us to obtain experimental information or by comparison to analogous molecules.