9.1. Lewis Electron Dot Structures http://www.ck12.org
FIGURE 9.1
Electron sharing in a water molecule.As you can see, there are two pairs of electrons not involved in covalent bonding. These unbonded pairs of electrons
are known aslone pairsand contribute to the overall shape of the molecule. Similarly, nitrogen needs three electrons
to complete its valence shell, so it tends to make three covalent bonds, with one lone pair of non-bonding electrons
left over:
Again, each of the lines stands for apairof bonding electrons (a single bond), and the lone pair on nitrogen is drawn
as two dots.
Double and Triple Bonds
So far we have considered only single bonds, formed by the sharing of one electron from each atom. Many molecules
containdouble bonds, in which each atom shares two electrons, ortriple bonds, in which each atom shares three
electrons. These are represented by drawing two or three lines in between the bonded atoms. For example, a carbon-
carbon double bond can be written as C::C or C=C. A carbon-carbon triple bond is shown as C:::C or with three lines
between the two carbon atoms, as seen in the structure of an organic molecule called acetylene (shown inFigure
9.2).
FIGURE 9.2
Acetylene moleculeSteps for Drawing Lewis Structures
- Identify the atoms that are participating in a covalent bond.