Formal positive charge

If carbon has a positive formal charge, then it has only three electrons (it is supposed to have four electrons, because carbon is in Column 4A of the periodic table). Since it has only three electrons, it can form only three bonds. That s it. So, a carbon with a positive formal charge will have only three bonds, and you should keep this in mind when counting hydrogen atoms ... 

Answer The oxygen atom has a positive formal charge and three bonds. You should try to get to a point where you recognize that this must mean that the oxygen atom has one lone pair ... 

When an Inner atom has a positive formal charge, a... 

To summarize, the provisionai Lewis structure reached after Step 4 may not aiiocate an optimum number of eiectrons to one or more of the inner atoms. The eiectron distribution must be optimized when any inner atom does not have at ieast eight eiectrons or when an inner atom from beyond the second row has a positive formal charge. In either of these situations, a more stabie structure resuits from transferring nonbonding electrons from outer atoms to inner atoms to create doubie bonds (four shared electrons) or triple bonds (six shared electrons). 

Compare the total number of electrons that appear to be on each atom to the number of valence shell electrons that it normally has. If the number of electrons in the valence shell is greater than indicated in step 3, the atom appears to have lost one or more electrons and has a positive formal charge. If the number indicated in step 3 is larger than the number in the valence shell, the atom appears to have gained one or more electrons and has a negative formal charge. 

Both structures II and III have an arrangement of atoms that places a positive formal charge on atoms that are higher in electronegativity than carbon. Consequently, the most stable arrangement of atoms is as shown in structure I. Some compounds containing the ion having structure III (the fulminate ion) are known, but they are much less stable than the cyanates (structure I). In fact, mercury fulminate has been used as a detonator. 

In this case, even with there being one double bond, the formal charge on the sulfur atom is +2, so structures that show two double bonds are possible, which can reduce further the positive formal charge. In order for structures such as... 

Structure III makes virtually no contribution because of the positive formal charges on adjacent atoms and the overall higher formal charges. In HN3, the bond lengths are... 

The nitrogen atom is triply bonded to the oxygen atom and both atoms in the structure possess a lone pair of electrons. This gives each atom an octet and a positive formal charge appears on the oxygen atom. 

The second theoretical development is due to Sokolov (p. 385). This writer attempts to calculate the additional energy of the H-bond in terms which appear to correspond to our effects (A), (B) and (C). The effective parameter is the positive formal charge Z on the hydrogen atom. Plausible variations of the various terms with Z and with the bond distances enable the change of frequency v in the 0—H valence vibration to be estimated, in good agreement with experiment. 

If the atom has more electrons in the molecule than when it is a free, neutral atom, then the atom has a negative formal charge, like a monatomic anion. If the assignment of electrons leaves the atom with fewer electrons than when it is free, then the atom has a positive formal charge, as if it were a monatomic cation. Mathematically, we write... 

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