code: def get_element_mass_dictionary(self):
          
  
          element_symbols = self.material.elements
          element_masses = self.get_element_masses()
  
          return {s: m for s, m in zip(element_symbols, element_masses)}
docs: Determine the masses of elements in the package and return as a
          dictionary.
  
          :returns: Dictionary of element symbols and masses. [kg]