How To Draw Complicated Lewis Structures

An outline of how to detemine the "best" Lewis structure for an instance, NO_three ^- is given below:

one. Determine the full number of valence electrons in a molecule

2. Draw a skeleton for the molecule which connects all atoms using only unmarried bonds. In simple molecules, the atom with the most available sites for bondng is unremarkably placed central. The number of bonding sites is detemined by considering the number of valence electrons and the ability of an atom to expand it's octet. As you become meliorate, you will exist able to recognise that certain groups of atoms prefer to bond together in a sure way.

3. Of the 24 valence electrons in NO₃ ^-, half-dozen were required to make the skeleton. Consider the remaining eighteen electrons and identify them so as to fill the ocets of as many atoms equally possible (start with the most electronegative atoms first then proceed to the more electropositive atoms).

4. Are the octets of all the atoms filled? If not then fill up the remaining octets by making multiple bonds (make a lone pair of electrons, located on a more than electronegative cantlet, into a bonding pair of electrons that is shared with the atom that is electron defficient).

v. Check that you have the lowest FORMAL CHARGES possible for all the atoms, without violating the octet rule; (valence e-) - (1/ii bonding due east-) - (solitary electrons).

IMPORTANT : no Lewis diagram is complete without formal charges. Lewis diagrams are drawn to examine mechanisms so knowing which parts of a molecule are electron defficient (+) and which are electron rich (-) is vital.
Information technology is best to have a formal charge of 0 for as many of the atoms in a construction every bit possible.
If a formal charge of 1- is located adjacent to a formal charge of ane+, the formal charges can usually be minimized by having a lonely pair of electrons, located on the atom with the 1- accuse become a bonding pair of electrons that is shared with the cantlet that has the 1+ formal accuse (this tin can be visualised in the same fashion as the formation of multiple bonds were higher up).

Caution : octets can be expanded to minimise formal charges but but for atoms in the second row of the periodic table (where north=3 or greater). For example in our example, N cannot aggrandize its octet so keeps a formal charge of ane+ and both singly bonded oxygens a formal charge of one-. If our molecule were And so₃ , however, it would be possible to minimize all formal charges by having the sulfur expand its octet.

6. You may observe that the best Lewis diagram (the one with the lowest formal charges and all octets satisfied) is given in a number of dissimilar ways. For NO₃ ^-, 3 different diagrams are given below. From left to right they start with the nearly complete Lewis diagram to the near simplified.