Originally Posted by **starrysky** ZnO is a semiconductor material that has a band gap of 310 kJ/mol. What is the longest wavelength of light, in nm, that will excite an electron from the valence band to the conductance band? |

Your unit is wrong. A band gap is defined as the energy to promote an electron from the top/bottom of one band (valence, conduction, etc) to the bottom/top of another. kJ/mol is not an energy.

310 kJ is an awesomely huge band gap. Might we be talking about 310 x 6 x 10^{-23} kJ? That's an awesomely small band gap. I'll leave that one for you to talk to your instructor about.

Anyway, we know that the energy of the photon is $\displaystyle E = \frac{hc}{\lambda}$. So the largest possible $\displaystyle \lambda$ will be for the smallest possible energy jump. So what's E?

-Dan