# Homework Help: Wavefunction of a one electron species?

1. Jan 17, 2010

### ekmcmurderme

1. Compute the ground state energy and first excited state energy of a one electron species with Z = 5.
E = -(Z^2*e^2)/(8*pi*epsilon 0*a*n^2).

2. I cannot for the life of me figure out how to find "a."

3. I know from the question that Z=5 and I assume e=-1.6e-19 C because the pi epsilon 0 thing would go with permittivity constant which allows unit cancellation and n=1 for ground state and n=2 for first excited state. The only problem is I cannot figure out what "a" is so I cannot attempt to answer the question. Help?

2. Jan 17, 2010

### vela

Staff Emeritus
I'm guessing that by "one electron species," you mean one-electron atoms. If that's the case, $a$ probably stands for the Bohr radius. You should be able to find its definition in your textbook or notes.

3. Jan 17, 2010

### ekmcmurderme

That makes sense because I saw something about that when I was using google and wikipedia to try to figure it out but the problem is this class doesn't have a textbook and we haven't had notes because we have only met once. Can you help me figure out how to find the Bohr's radius?