code: @Override
      public DescriptorValue calculate(IAtom atom, IAtomContainer container) {
          int period;
          String symbol = atom.getSymbol();
          period = periodicTable.get(symbol);
          return new DescriptorValue(getSpecification(), getParameterNames(), getParameters(), new IntegerResult(period),
                                     NAMES);
      }
docs: This method calculates the period of an atom.
  
  @param  atom              The IAtom for which the DescriptorValue is requested
  @param  container         Parameter is the atom container.
  @return                   The period