Formal charge ammonium cation

Throughout this course, we deal not only with molecules, but also with polyatomic cations and polyatomic anions. Examples of polyatomic cations are the hydronium ion, HgO, and the ammonium ion, NH4. An example of a polyatomic anion is the bicarbonate ion, HC03. It is important that you be able to determine which atom or atoms in a molecule or polyatomic ion bear the positive or negative charge. The charge on an atom in a molecule or polyatomic ion is called its formal charge. To derive a formal charge. 

Important derivatives of ammonia are the tetraalkyl ammonium salts. The cation in these salts has four organic groups attached to the nitrogen atom and is called a quaternary ammonium ion. In a quaternary ammonium ion, the nitrogen atom has a formal charge of -l-l. Two examples of such cations are shown in the margin. 

Any ionic solid, such as ammonium chloride, is called a salt. In a formal sense, a salt can be thought of as the product of an acid-base reaction. When an acid and base react, they are said to neutralize each other. Most salts containing cations and anions with a single positive and negative charge are strong electrolytes—they dissociate nearly completely into ions in dilute aqueous solution. Thus, ammonium chloride gives NH and Cl- in water ... 

The cation cts-fNHj Ch OHJCrlNHjX N CHjCHjNHj)64 is formally a +6 charged species, but since the charge of the ammonium group is remote from the hydroxo bridge, it is reasonable that the acidity of the latter is comparable to that for the +5 charged rhodo ion. 

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