Q:

Identify atoms in chemical equation

I am trying to represent an exchange reaction in N2 + N, where the reactant atomic N is swapped for one in N2.  I'm using the mhchem package, and currently have the following:
\documentclass{article}
\usepackage[version=4]{mhchem}
\begin{document}

The exchange reaction is:

\begin{align}
   \ce{ N^{(1)} \bond{1} N^{(2)} + N^{(3)} 
     -> N^{(1)} \bond{1} N^{(3)} + N^{(2)} }
\end{align}

\end{document}

I'm unhappy with this for several reasons. 

It's not immediately clear that the superscript numbers are atomic identifiers. 
The spacing between bonded atoms is about the same as the spacing between molecules (+ vs -).  I think having more space between molecules or less space between bonded atoms would help. 

Perhaps I just need to fiddle with the spacing, especially because the superscripts are adding space.  What is the best way to do that inside an mhchem equation? 
Alternatively, I could completely ditch the superscript atomic identifiers and use a more clear distinction.  Obviously, I need to specify that the reactant atomic N is now a component of N2, but how?  Any suggestions are welcome. 
Edit 1
Removing the parenthesis and the space between bonds, as suggested in the comments,
\documentclass{article}
\usepackage[version=4]{mhchem}
\begin{document}

New:
%
\begin{align*}
   \ce{ N^{1}-N^{2} + N^{3}
     -> N^{1}-N^{3} + N^{2} }
\end{align*}

Old:
%
\begin{align*}
   \ce{ N^{(1)} \bond{1} N^{(2)} + N^{(3)}
     -> N^{(1)} \bond{1} N^{(3)} + N^{(2)} }
\end{align*}

\end{document}

This is clearly better, but the spacing before the bond (due to the superscript) still looks too large.  What is the best way to fiddle with this? 

A:

First of all: don't leave spaces around the bonds:
\documentclass{article}
\usepackage[version=4]{mhchem}
\begin{document}

\ce{
     N^{(1)} \bond{1} N^{(2)} + N^{(3)} 
  -> N^{(1)} \bond{1} N^{(3)} + N^{(2)}
}

\ce{
     N^{(1)}\bond{1}N^{(2)} + N^{(3)} 
  -> N^{(1)}\bond{1}N^{(3)} + N^{(2)}
}

\end{document}

Instead of \bond{1} it also suffices to input -:
\documentclass{article}
\usepackage[version=4]{mhchem}
\begin{document}

\ce{
     N^{(1)}\bond{1}N^{(2)} + N^{(3)} 
  -> N^{(1)}\bond{1}N^{(3)} + N^{(2)}
}

\ce{
     N^{(1)}-N^{(2)} + N^{(3)} 
  -> N^{(1)}-N^{(3)} + N^{(2)}
}

\end{document}

Personally I'd also leave the parentheses away.  It is not uncommon to mark different substituents with supersctipt numbers (cf.  \ce{R^1}).  In my opionion the message becomes even clearer without the parentheses:
\documentclass{article}
\usepackage[version=4]{mhchem}
\begin{document}

\ce{
     N^{(1)}-N^{(2)} + N^{(3)} 
  -> N^{(1)}-N^{(3)} + N^{(2)}
}

\ce{
     N^{1}-N^2 + N^3 
  -> N^{1}-N^3 + N^2
}

\end{document}

Of course colors also work (unless you're colorblind):
\documentclass{article}
\usepackage[version=4]{mhchem}
\usepackage{xcolor}
\begin{document}

\ce{
     {\textcolor{red}{N}}-\textcolor{blue}{N} + \textcolor{green}{N} 
  -> {\textcolor{red}{N}}-\textcolor{green}{N} + \textcolor{blue}{N}
}

\end{document}

And just as a comparison using chemfig:
\documentclass{article}
\usepackage{chemfig}
\begin{document}

\schemestart
  \chemfig{N^1-N^2} \+ \chemfig{N^3}
  \arrow
  \chemfig{N^1-N^3} \+ \chemfig{N^2}
\schemestop

\end{document}

Here the length of bond and arrow is easily customizable.