# High n transitions (eg 109-108) are observed in excited He..

1. Oct 31, 2016

### Poirot

1. The problem statement, all variables and given/known data
Transitions between n=109 to n=108 have been observed in highly excited helium atoms and in this case the Bohr model is a valid approximation. Why is this?

2. Relevant equations
N/A

3. The attempt at a solution
I'm having some problems with this question and it probably comes down to a lack of understanding.
I think it may be because the electron that undergoes this transition is so far from the nucleus/the other e- that we can assume they don't interact with one another (such that Bohr model is valid) but I'm not overly sure/don't understand enough.

Any help would be greatly appreciated thank you!

2. Oct 31, 2016

The other electron is near the nucleus, as you said. What charge does the nucleus have? What charge does the combination of nucleus plus inner electron have? The two electrons will interact, but the interaction will be one of a Coulomb type interaction, where the inner electron is combined with the nucleus rather than moving freely in a somewhat unpredictable manner. If you were to quantify the Bohr model, to compute the wavelength of this transition, what $Z$ (atomic number of nucleus) would you use? Additional item, does the increased mass of the nucleus have any appreciable effect? What is the mass that is used in the Bohr model? $\\$ Note: The Bohr atom model uses three equations: (c.g.s. units) 1) Angular momentum $L=mvr=n \hbar$ $\$ 2) Coulomb force =centripetal force for circular motion $Ze^2/r^2=mv^2/r$ $\$ 3) Energy $E_n=(1/2)mv^2-Ze^2/r$. Solve for unknowns $E_n, \, v, \, r$. Are these equations equally valid for this modified helium atom as they are for a hydrogen atom?