I experienced this question and I was interested in the answer as well. I teach high college (IB) chemistry and physics and also have never ever encountered a nationwide curriculum that calls for this. Are you a college level student?

I did a tiny research which evidenced my thoughts the this is one incredibly complex problem. If you to be presented with a streamlined equation by her instructor, please pass this on and also we will shot to assist you.

You are watching: How to calculate second ionization energy

The paper I discovered that to be most carefully related to your inquiry is situated at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3671562/

As you can see, the mathematics is quite complex.

You should know that the second ionization power for He will be much greater than the first. This is since 1) the second electron is currently being pulled away from a positive ion2)helium"s two electrons are both situated in the 1s orbital and when both existing repel each various other which provides removing the very first one less complicated than the second.

Good luck

Answer connect

Stefan V.
Apr 9, 2015

Bohr"s equation can not be applied to multi-electron atoms like helium due to the fact that it just cannot account for experimental data.

It is valid for hydrogen-like atoms, however, this gift the factor for why the second ionization power of helium is calculate correctly.

In helium"s case, Bohr"s equation predicts the very same value for both the first, and also the second ionization energies: 5276 kJ/mol, with only the 2nd ionization energy being correct.

For multi-electron atoms, you need to replace #Z# v #Z_"eff"#, the effective nuclear charge.

So, the equation becomes

#E_n = -R_H * Z_"eff"^(2)/n^(2)#, where

#-R_H = 2.178 * 10^(-18)"J"#

Here"s where it gets interesting. Ns won"t get in details around it, but, according to calculations, helium"s second 1s electron feels an reliable nuclear fee equal come 1.7 - more on that here:


However, when you plug 1.7 right into the above equation you gain a first ionization energy around equal to 3791 kJ/mol, which is closer come the experimental value that 2372 kJ/mol, yet not fairly the same.

If you occupational backwards and also plug the speculative 2372 kJ/mol very first ionization power into the equation and solve for #Z_"eff"#, you"d acquire a value of 1.34, reduced than the 1.7 worth the calculations would certainly predict.

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Like David said in one of the answers currently posted, the calculations because that the an initial ionization energy are very facility (very, an extremely messy), so i don"t understand if you"d ever be inquiry to in reality go v them and get the elusive 2372 kJ/mol value.