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
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.