Hi, Which of ZnS and CdSe will have the larger band gap energy, explain. The answer is given as Zinc sulfide will have a larger band gap energy than cadmium selenide. Both are II-VI compounds, and Zn and S are both higher vertically in the periodic table than Cd and Se. In moving from bottom to top up the periodic table, band gap energy increases. I don't understand why moving from bottom up in the periodic table increases bang gap energy. Is it because electronegativity increases? Would really appreciate if anyone could explain this! Thank you v much in advance.