Nitrogen atom with formal charge

Compounds containing a nitrogen atom with four attached groups also exist, but the nitrogen atom must carry a formal positive charge. Such compounds are called quaternary ammonium salts. 

Figure 3.1 Electrostatic potential maps for BF3, NH3, and the product that results from reaction between them. Attraction between the strongly positive region of BF3 and the negative region of NH3 causes them to react. The electrostatic potential map for the product for the product shows that the fluorine atoms draw in the electron density of the formal negative charge, and the nitrogen atom, with its hydrogens, carries the formal positive charge.

The Nitrate Ion (NO3 ) Let us next consider the nitrate ion (NO3 ), an ion that has oxygen atoms with unshared electron pairs. Here we find that the nitrogen atom has a formal charge of +1, that two oxygen atoms have formal charges of — 1, and that one oxygen has a formal charge equal to 0. 

A NITROGEN ATOM WITH A NEGATIVE CHARGE WILL HAVE N. LONE PAIR(S) A NITROGEN ATOM WITH NO FORMAL CHARGE WILL HAVE V. N. LONE PAIR(S) A NITROGEN ATOM. , WITH A POSITIVE / CHARGE WILL HAVE LONEPAIR(S) —... 

The green oxygen m Figure 1 5 owns three unshared pairs (six electrons) and shares two electrons with nitrogen to give it an electron count of seven This is one more than the number of electrons m the valence shell of an oxygen atom and so its formal charge is —1... 

From all of the cases above (oxygen, nitrogen, carbon), you can see why you have to know how many lone pairs there are on an atom in order to figure out the formal charge on that atom. Similarly, you have to know the formal charge to figure out how many lone pairs there are on an atom. Take the case below with the nitrogen atom shown ... 

The study of compounds containing pentacoordinate silicon atoms currently represents one of the main areas of research in silicon chemistry. This is evident from the numerous reviews and proceedings published on this topic in recent years.112 Most of the pentacoordinate silicon compounds described in the literature are either salts with A5.S7-silicate anions or neutral silicon complexes with a 4+1 coordination to silicon. This review deals with a completely different class of pentacoordinate silicon compounds zwitterionic A S /-silicatcs. These molecular compounds contain a pentacoordinate (formally negatively charged) silicon atom and a tetracoordinate (formally positively charged) nitrogen atom. 

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