Lewis Dot Structures of Molecules
Lewis took the Octet Rule and applied it to molecules. For instance, we already know that a chlorine atom is unstable because it has only 7 electrons, and that it can become stable if it can steal an electron from another atom to become an -1 ion. We also know that chlorine appears in nature as Cl2 not as single atoms of chlorine and that the molecule has a single bond.
Lewis deduced that if electrons involved in the tug-o-war each counted for both atoms, then each atom would have an octet and would be stable.
Using this logic, we can draw the LDS's for other molecules, like OCl2:
Lewis also determined that hydrogen does not obey th octet rule, but rather follows its own “duet rule.” Of course this makes sense when we remember that hydrogen only has one orbital (the 1s) which can only hold two electrons. So LDS's that involve hydrogen (H2, CH4) look like this:
Remember that Lewis didn't care how the electron dots were placed around the atomic symbol. That means that all three of the following are correct LDS's for water:
The last of these is a bit disorganized but it shows, correctly, that water has one oxygen bonded to two different hydrogen atoms. For the sake of clarity we will, in the future, arrange the electrons so that our diagrams are as neat as possible.
It is also acceptable to replace any pair of electrons (whether in a bond or attached to a single atom) with a dash (—), as shown here: