A second filter is the electronegativity balance, which requires that the most electronegative ion has the most negative charge in the compound. Using the Pauling electronegativity scale 8 , χ anion -χ cation > 0. For example, the pnictide semiconductor GaSb is allowed by this filter (χ anion(Sb)χ cation(Ga) = 0.24), while the oxide catalyst Sb2O3 is also allowed, where Sb is the cation (χ anion(O)χ cation(Sb) = 1.39). This filter helps distinguish between allowed and forbidden inorganic stoichiometries based on electronegativity considerations, ensuring that the composition contains sensible combinations of species.