3.1: Lewis Electron-Dot Diagrams

• Gilbert Lewis Newton introduced a simple way to show the bonding between atoms in a molecule through Lewis electron dot diagrams.
• Valence electrons are represented as dots and when two electrons are paired (lone pairs), they are represented by two adjacent dots located on an atom.
• When two paired electrons are shared between atoms (bonds), they are shown as lines.
• Lewis electron dot diagrams allow us to show how atoms are connected and to predict the shape of the molecule using the valence shell electron repulsion theory (VSEPR).
• The octet rule states that atoms form bonds to achieve eight electrons in their valence shell.
• The first row elements, H and He, are exceptions to the octet rule although they still have a full valence shell.
• Hypovalency is when an atom has partially-filled valence shells, such as a carbocation.
• Hypervalency is a case where an element has more than eight electrons in its valence shell, common for larger atoms.
• When an atom is part of a molecule, all electrons that are associated with the atom are counted as contributing to the atom's valence, including electrons that are lone pairs and shared in bonds.
• Electrons in valence (octet) = total unbound electrons in the atom + total bonded electrons