code: private static int electronsForAtomType(IAtom atom) {
          Integer electrons = TYPES.get(atom.getAtomTypeName());
  
          if (electrons != null) return electrons;
  
          try {
              IAtomType atomType = AtomTypeFactory.getInstance("org/openscience/cdk/dict/data/cdk-atom-types.owl",
                      atom.getBuilder()).getAtomType(atom.getAtomTypeName());
              electrons = atomType.getProperty(CDKConstants.PI_BOND_COUNT);
              return electrons != null ? electrons : 0;
          } catch (NoSuchAtomTypeException e) {
              throw new IllegalArgumentException(e);
          }
      }
docs: The number of contributed electrons for the atom type of the specified
  atom type.
  
  @param atom an atom to get the contribution of
  @return the number of electrons