Lewis Theory of Bonding
Chemical bonding is at the heart of understanding chemistry. The Lewis Theory of Bonding essentially combined
observations at the time about chemical bonding together. Not only was it essential in understanding how elements
bonded, it provided a visual representation for them. These Lewis dot structures are a simplistic way of representing
the electrons in molecules. This theory also helped to define formal charge and resonance.
Understanding of electronegativity and electron affinity will be useful before understanding Lewis Theory of Bonding.
Introduction
The Lewis Theory used observations from chemists and physicists to form a theory about chemical bonding. This
work was essentially a compilation of the knowledge at the time. It revolved around the importance of valence
electrons in chemical bonding. These are the electrons that are in the outermost shell. For example Na may have 11
electrons, but only one is a valence electron, the one in 3s1. Meanwhile P has 15 electrons, but has five valence
electrons, 3s2 and 3p2. The bonding of an element is based on how they fill their octets i.e. achieve a noble gas
electron configurations.
Lewis went on to explain how certain elements such as Boron did not necessarily follow these same rules. He
explicitly defined two ways electrons were used to form bonds. These were ionic (complete transfer of electron) and
covalent (sharing of electrons) bonding. He added to his covalent bonding theory that atoms can have a double or
triple bonds with other atoms when electrons are shared. A single bond consists of two electrons sharing between
two atoms, double bond consists of four electrons sharing between two atoms, and triple bond consists of six
electrons sharing between two atoms. In both cases Lewis dot structures were used to visualize the the bonding of
the atoms in case of electron sharing or electron transfer.
Basic Lewis Dot Structures
There are two basic types of bonding that form the basis of the Lewis theory and it is important to understood before
one can begin to draw Lewis dot structures.
Ionic Bonding
In ionic bonding one element is much more electronegative then another element. In other words, the
electronegative atom wants an electron much more than the other element; thus, the element with a positive charge
loses electron and the element with the negative charge gains an electron. These two elements then become
attracted to each other because of Coulomb’s Law which states that there is electrostatic interaction between
particles that are electrically charged, in this case the electrons describes the charge of the atom. The atom that loses
electrons is electron deficient; thus, the atomic charge will be positive. The atom that gains electrons has excess of
electrons; thus, the atomic charge will be negative. This attraction between the elements brings them together to form
an ionic bond. An example of an ionic compound is shown below.
