Achieve Hw #12

[Ella_hou]

Can someone explain the steps to work out this question?

"The electron affinity of thulium has been measured by a technique known as laser photodetachment electron spectroscopy. In this technique, a gaseous beam of the anions of an element is bombarded with photons from a laser. Electrons from the anion are then ejected and their energies are detected. The incident radiation had a wavelength of 1064 nm, and the ejected electrons were found to have an energy of 0.137 eV. The electron affinity is the difference in energy between the incident photons and the energy of the ejected electrons. Determine the electron affinity of thulium in units of electron volts per atom."

I know I have to convert electron volt to joules and I also have to determine the energy of the light using E=hc/lamba.

[105605391]

For this question, I found it helpful to mentally picture the gaseous beam of anions as the metal used in the photoelectric experiments in the textbook. So with this, we are given the initial wavelength before the anion is stuck and the energy of the ejected electron, and we have to use the wavelength to find the initial E of the laser. Once you find the initial wavelength energy you are going to subtract the two energy values (prestrike wave and poststroke e-) to find the electron affinity. To find the two answers convert to eV if you were using J and for the final answer, you are going to be using Avogadro's number.

[RossLechner3E]

The general goal here is to obtain the energy of the incident radiation in ev then to subtract the given electron value to obtain the electron affinity. First convert the wavelength from nanometers to meters since we use E=h(c/lambda) which is 10^-9. Then plug that info into the equation, this gives the energy in J however, we want it in ev so we convert appropriately and then subtract the electrons energy from this value and this yields the electron affinity.

[Sunny Xiao 1A]

I was confused too at first, but realized it tells you exactly what to find when it says what electron affinity is. You just need to subtract the given energy of electrons (after converting it from eV to J) from the energy of the incident photons (E=hc/lambda). Then, you convert the final answer back to eV. For the second part, you just need to convert the Joules answer you got to kJ and multiply by Avogadro's constant (6.022*10^23 atoms/mol).