[Historical note: My presentation of G. N. Lewis'
bonding theory does not cling tightly to the historical record.
I have added ideas that came from others (notably I. Langmuir),
and I have quashed all of Lewis' major blunders. The result is "Lewis
theory" as modern chemists recognize it, but it isn't history.]
Lewis' theory consists of the ideas in the following list. You can jump directly to a detailed essay by clicking on the appropriate title, or you can read the essays in order by clicking on the Next button.
- Valence electrons
Atoms contain two kinds of electrons, core and valence.
Valence electrons, by definition, are the only ones affected
by chemical bonding and chemical reactions.
- Inert gas electron configurations
Inert gas atoms are chemically unreactive because their
valence electrons are configured in a way that is unresponsive
to other atoms. This electron pattern is called a Lewis
octet. Other atoms exchange electrons and form bonds
because this reconfigures their valence electrons into inert
gas-like patterns, in other words, into Lewis octets.
- Ions and ionic bonds
Some atoms create Lewis octets by transferring electrons
to or from other atoms. If an atom gains an electron, it
becomes a negatively charged anion. If it loses an
electron, it becomes a positively charged cation.
Oppositely charged ions form compounds that are held together
by ionic bonds.
- Covalent bonds
Other atoms create Lewis octets by sharing pairs of electrons
with other atoms. The shared electron pair is "seen"
by both atoms and creates an attractive force between them.
This attraction is called a covalent bond.
- Transfer or share?
Whether an atom transfers or shares electrons is dictated
by the change in atom energy. Electrostatic forces make
electron transfer most favorable for singly charged ions,
like Na+ and Cl-.
More highly charged ions are hard to make, and electron
sharing becomes a more favorable option.