code: AtomSymbol generateSymbol(IAtomContainer container, IAtom atom, HydrogenPosition position, RendererModel model) {
          if (atom instanceof IPseudoAtom) {
              IPseudoAtom pAtom = (IPseudoAtom) atom;
              if (pAtom.getAttachPointNum() <= 0) {
                  if (pAtom.getLabel().equals("*")) {
                      int mass = unboxSafely(pAtom.getMassNumber(), 0);
                      int charge  = unboxSafely(pAtom.getFormalCharge(), 0);
                      int hcnt    = unboxSafely(pAtom.getImplicitHydrogenCount(), 0);
                      int nrad = container.getConnectedSingleElectronsCount(atom);
                      if (mass != 0 || charge != 0 || hcnt != 0) {
                          return generatePeriodicSymbol(0, hcnt,
                                                        mass, charge,
                                                        nrad, position);
                      }
                  }
                  return generatePseudoSymbol(accessPseudoLabel(pAtom, "?"), position);
              }
              else
                  return null; // attach point drawn in bond generator
          } else {
              int number = unboxSafely(atom.getAtomicNumber(), Elements.ofString(atom.getSymbol()).number());
  
              // unset the mass if it's the major isotope (could be an option)
              Integer mass = atom.getMassNumber();
              if (number != 0 &&
                  mass != null &&
                  model != null &&
                  model.get(StandardGenerator.OmitMajorIsotopes.class) &&
                  isMajorIsotope(number, mass)) {
                  mass = null;
              }
  
              return generatePeriodicSymbol(number, unboxSafely(atom.getImplicitHydrogenCount(), 0),
                                            unboxSafely(mass, -1), unboxSafely(atom.getFormalCharge(), 0),
                                            container.getConnectedSingleElectronsCount(atom), position);
          }
      }
docs: Generate the displayed atom symbol for an atom in given structure with the specified hydrogen
  position.
  
  @param container structure to which the atom belongs
  @param atom      the atom to generate the symbol for
  @param position  the hydrogen position
  @param model     additional rendering options
  @return atom symbol