Starting with a structure indicating only atom connections (single bonds),
you can practice constructing a Lewis dot structure.
Just click on the atom or bond you wish to modify.
Nonzero formal charges are indicated for each atom in the structure
once the total number of electrons is correct.
A recommended procedure might be:
- Count the total number of valence electrons (N) needed to account for the atoms (based on the column of the atom in the periodic table) and charge (add one electrons for each negative charge; subtract one electron for each positive charge).
- Draw the framework with single bonds. Some knowledge of the way the atoms are connected may be required.
- Using lone pairs, complete octets around the noncentral atoms.
- Count the number of electrons depicted
(two for each bond and two for each lone pair).
If this number is less than N,
then add electrons to the central atom until the total
number of electrons depicted is N.
At this point you have what we call a "sigma" structure (because all the electrons are present and the bonds now correspond to all of the "sigma" bonds in the actual molecule).
- If the octet rule is not satisfied for the central atom and lone-pair electrons are nearby, use those electrons to make double or triple bonds to the central atom.
- Indicate any formal charge by formally allocating every electron to a single atom. (Singly bonded oxygen will require a negative charge, for example.)