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# Worked example: Calculating the maximum wavelength capable of ionization

If a photon has enough energy, it can completely remove an electron from an atom or molecule. In this video, we'll use the light equations (E = h𝜈 and c = 𝜆𝜈) to calculate the longest photon wavelength capable of removing an electron from a single atom of silver. Created by Sal Khan.

## Want to join the conversation?

• Why does the question state "in the gas phase"? Would the energy be different in the solid?
• Yes, the ionization energy would be different for the same substance but for a solid versus a gas. To be able to compare the ionization energy between different atoms, they are done in the gas phase to make it standard. The gas phase is chosen specifically because the attraction between the atoms is minimal when in the gas phase compared to other phases.

Hope that helps.
• At Sal rewrites c/E/Planck's constant as c*Planck's constant/E. I don't understand how those two are equivalent
(1 vote)
• Sal is dividing two fractions.

λ = c/(E/h) is the same as c/1 ÷ E/h
Dividing fraction means you multiply by the reciprocal of the second fraction.
c/1 x h/E = (ch)/E

Hope that helps.
• Why does Sal round the energy? Wouldn't it be more precise to just straight up plug in the numbers into ch/((E/{Avogadro's Number})) => ch/v? In the problem sets, the solutions also tell us to round the energy first before plugging them in. Why is this?
(1 vote)
• You are correct in thinking that plugging everything as is given is more precise. I guess the sets are just there to make you understand the problems and not actually solve it in the most precise manner.