The ground state of the isotope of Technetium that has a mass number of 99 is denoted by Tc-99. The metastable state is denoted by Tc-99m. Are these considered to be two different nuclides, or just two states of the same nuclide? (I suspect that the definition of a nuclide takes into account not only mass number and atomic number, but energy state as well.) For that matter, are they considered to be the same isotope or two different isotopes?