Valence long pair

With the three carbons connected together, you ve used up four of the total valence electrons, because each bond counts as two electrons. You then can place the hydrogens around the carbons as you see fit, as long as you remember that each carbon can only have four total bonds or lone electron pairs. After placing the hydrogens, you end up with eight total bonds in the structure for a total of... 

There are some anomalies in Fig. 6.4, particularly for cations with s < 0.2 vu, and it is instructive to ask why these occur. There are several possible reasons. If a given pair of oxygen atoms is bonded to more than one cation, the effective valence is the sum of the effective valences of each of the cation O bonds, reducing the minimum length of the 0-0 contact, an elfect that has not been taken into account in preparing Fig. 6.4. For example, a weak cation may be chelated by N03 ions so that the shared 0-0 edges are only 215 pm long rather... 

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