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I am confused about the nature of the positive charge on the nitrogen atom in the diazonium ion. Where does it come from? That nitrogen atom has 4 bonds, but I cannot deduce whether one of them is dative, because the other nitrogen forms 3 normal bonds, and the carbon in the aromatic ring has no empty orbitals or lone pair of electrons. So how does that nitrogen form 4 bonds and how does it have a positive charge? Thanks

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In a diazonium, or rather any compound where nitrogen forms four bonds, the nitrogen has a positive formal charge.

The reason is simple, nitrogen used it's lone pair of electrons to make the fourth bond. This gives nitrogen a positive charge.

A more simple example is the ammonium ion. While ammonia has 3 bonds and 1 lone pair, the ammonium ion has 4 bonds, the lone pair from ammonia was shared with a proton to make the ammonium ion.

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    $\begingroup$ Thanks! I didn't read much about the concept of formal charges so I'll have a look at any page about it. $\endgroup$ – Fahd Al-Seba'ey Sep 9 '17 at 16:31
  • $\begingroup$ @FahdAl-Seba'ey Sure thing. If you think my answer is satisfactory, click the accept button. This lets everyone know you are satisfied and you got the answer you needed. $\endgroup$ – Pritt Balagopal Sep 9 '17 at 16:38
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    $\begingroup$ Note that formal positive is not the real positive. The entire species is positive, but the real positive charge is delocalized over the whole thing. $\endgroup$ – Zhe Sep 9 '17 at 17:56

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