9.1. Lewis Electron Dot Structures http://www.ck12.org
Each hydrogen atom will use its single electron to form a covalent bond with one of the unpaired electrons on the
oxygen atom. The resulting Lewis electron dot structure is:
Step 3: Think about your result.
The oxygen atom follows the octet rule with two pairs of bonding electrons and two lone pairs. Each hydrogen atom
follows the octet rule with one bonding pair of electrons.
Practice Problems- Draw the Lewis electron dot structure for each atom.
a. NH 3
b. CH 4
c. CH 2 Cl 2
Multiple Covalent Bonds
Some molecules are not able to satisfy the octet rule by making only single covalent bonds between the atoms.
Consider the compound ethene, which has a molecular formula of C 2 H 4. The carbon atoms are bonded together,
and each carbon is also bonded to two hydrogen atoms.
two C atoms = 2×4 = 8 valence electrons
four H atoms = 4×1 = 4 valence electrons
total of 12 valence electrons in the moleculeIf the Lewis electron dot structure were drawn with a single bond between the carbon atoms and lone pairs were then
added until all atoms satisfied the octet rule, it would look like this:
However, this Lewis structure is incorrect because it contains 14 valence electrons, and the atoms in this molecule
only have a total of 12 valence electrons available. The Lewis structure can be corrected by eliminating one lone
pair and moving another lone pair to a bonding position. Now, the two carbon atoms share two pairs of electrons
instead of just one.