For 10 points, name this quantity, the amount of energy needed to remove an electron from a gaseous atom or molecule.
Di-tungsten tetra(hpp) has the lowest known value of this quantity for a stable material. This quantity is equal to the negative energy of the HOMO according to Koopmans' theorem. Within the Bohr model, this quantity equals negative atomic number squared times 13.6 divided by n squared. With some exceptions like aluminum and gallium, this quantity increases toward the right within a period. For 10 points, name this quantity, the amount of energy needed to remove an electron from a gaseous atom or molecule.
Di-tungsten tetra(hpp) has the lowest known value of this quantity for a stable material.
first ionization energy