public RBond addRBond(Atom a1, Atom a2) {
		RBond rbond = new RBond(a1, a2);
		rbond.setLength(a1.distance(a2));
		if (model.addRBond(rbond)) {
			viewer.addRBond(a1, a2);
			model.formMolecules();
			model.notifyChange();
		}
		return rbond;
	}