How do i find the ionization level of Helium

[jimmersz]

Homework Statement

What is the ionization energy for He+ Z=2

Homework Equations

E = -13.6 z^2 / n^2

The Attempt at a Solution

I plugged 2 in for Z and 1 in for n, and got 54.4 eV. I checked many charts and it said the ionization energy for Helium was around 24.6 eV.

 

[hage567]

Well, I think you came up with the right answer. Are you sure that's what the chart said?

 

[jimmersz]

The chart had 24.6, but maybe that isn't for Helium Ions.

 

[Sean Torrebadel]

Bohr's theory is flawed

If you try to use a Bohr equation, which uses Z squared, you cannot calculate the ionization energy of a neutral atom such as Helium I. The problem is that Bohr's theory has never been show to successfully calculate the ionization of Helium. However, the second ionization energy does calculate as 54.42. It is interesting that the third ionization energy of Lithium, the fourth of Beryllium and so forth do work with Z squared in the equation. Perhaps quantum mechanics (perbutation theory) succeeds where Bohr failed-I'm not sure.
Bohr assumed that Z represents the nuclear charge of the atom. He also believed that electron-electron repulsion would interfere with the calculation. Even when considering this interference, Bohr was never able to reach an accurate value for Helium's first ionization energy- which is actually 24.5874.
I can only speculate, at this point, that Z is not the nuclear charge, but the ionic charge of the nucleus. And that it is only when one electron is left that this value is qualified.
Bohr was only able to use his theory to explain the spectra of Hydrogen, and Hydrogen-like atoms-atoms stripped of all but one electron. Accordingly, he could only solve for the ionization energies of He II, Be III, Li IV, etc Where II is one electron removed, III is two electrons removed etc.