9 Electron dot structures & formal charge
9.1 Electron Dot Structures
Electron dot structures, also calledLewis structures, give a representation of the valence
electrons surrounding an atom.
Each valence electron is represented by one dot, thus, a lone atom of hydrogen would be
drawn as anHwith one dot, whereas a lone atom of Helium would be drawn as anHewith
two dots, and so forth.
Representing two atoms joined by a covalent bond is done by drawing the atomic symbols
near to each other, and drawing a single line to represent a shared pair of electrons. It
is important to note: a single valence electron is represented by a dot, whereas a pair of
electrons is represented by a line.
The covalent compound hydrogen fluoride, for example, would be represented by the symbol
Hjoined to the symbolFby a single line, with three pairs (six more dots) surrounding the
symbolF. The line represents the two electrons shared by both hydrogen and fluorine,
whereas the six paired dots represent fluorine’s remaining six valence electrons.
Dot structures are useful in illustrating simple covalent molecules, but the limitations of
dot structures become obvious when diagramming even relatively simple organic molecules.
The dot structures have no ability to represent the actual physical orientation of molecules,
and they become overly cumbersome when more than three or four atoms are represented.
Lewis dot structures are useful for introducing the idea of covalence and bonding in small
molecules, but other model types have much more capability to communicate chemistry
concepts.