code: public IAtom getPlacedHeavyAtom(IAtomContainer molecule, IAtom atom) {
          List<IBond> bonds = molecule.getConnectedBondsList(atom);
          for (IBond bond : bonds) {
              IAtom connectedAtom = bond.getOther(atom);
              if (isPlacedHeavyAtom(connectedAtom)) {
                  return connectedAtom;
              }
          }
          return null;
      }
docs: Returns a placed atom connected to a given atom.
  
  @param molecule
  @param  atom  The Atom whose placed bonding partners are to be returned
  @return       a placed heavy atom connected to a given atom
  author:      steinbeck