A WORKED EXAMPLE

Consider nitrate, [NO3]–. Generally, it is best to draw the most electropositive atom in the middle first as the most electropositive atom can (coincidentally!) form more bonds, and with a low formal charge.

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After step 1, in which you draw one bond to each atom, it will look like A. It is not a valid Lewis structure because the sum of formal charges is –3 rather than –1.

The addition of one bond, step 2, will increase the formal charge by +2 to the correct value of –1 and thus generate a valid Lewis structure (B).

The lone pairs can now be placed, step 3, so that each atom obeys the octet rule (C).