code: private static int lonePairCount(IAtom atom) {
          // XXX: LONE_PAIR_COUNT is not currently set!
          Integer count = atom.getProperty(CDKConstants.LONE_PAIR_COUNT);
          return count != null ? count : -1;
      }
docs: Access to the number of lone-pairs (specified as a property of the
  atom).
  
  @param atom the atom to get the lone pairs from
  @return number of lone pairs