Simplified Rules for Lewis Dot Structures

H always has one bond. It is bound to the atom it follows unless it does not follow an atom and then it is bound to the atom after it. If it is not bound, H is either a free radical (H·) or it has charge.

C always has four bonds. These can be in the form of multiple bonds. For instance, one double bond and two single bonds is four. Whenever C has no charge, H is bound to it to give it four bonds. For instance, if a C has a double bond to C1 and a single bond to a C2, it must has an H if it does not have a charge. If C has only three bonds, it is either a free radical (example: H3C·) or it has charge.

O always has two bonds and two NB. The two bonds can be either two single bonds or a double bond. One of the NB can become a bond, but then the O has a positive charge. If O has only one bond and three NB, then it has a negative charge. It can also be a free radical if one of its NB is a single electron.

N always has three bonds and one NB. The three bonds can include multiple bonds. For instance, one double bond, one single bond and one NB. If a NB becomes a bond to give N four bonds, it has a positive charge. If it has only two bonds and two NB, then it has a negative charge. It can also be a free radical if it has three bonds and one NB loses an electron to become a single electron.

X always has one bond and three NB. Halogens are relatively common as free radicals. A free radical halogen has three NB and a single electron.

B always has three bonds and no NB (an empty orbital). It can have a fourth bond, but then it hasa negative charge.

Elements within a column behave similarly to each other and tend to follow the same rules. P and heavier elements can have 5 or 6 bonds. We will study them later.