The two electrons in helium are NOT equivalent. The first ionization potential (

Question

The two electrons in helium are NOT equivalent. The first ionization potential (energy required to remove the first electron) is 24.6 eV and the second ionization potential (energy required to remove the second and last electron) is 54.4 eV. The second ionization potential agrees very well with what is predicted by the hydrogen-like atom model and the general Rydberg equation, E = Z2 RH (1 / ni2 – 1 / nf2 ). Why do you think it takes about half the energy to remove the first electron, compared to the energy needed to remove the last electron?

Explanation / Answer

Because of inter electronic repulsions and shielding of one electron on other, the effective nuclear attraction is some how lower than the expected.

And one more thing in He number of electrons and number of protons are equal.

But, after removing the first electron, there is only one electron which does not experince any interelectronic repulsions, and also now it has only one electron but it is attracted by tow protons. So, the electron in He+ ion experiences more attraction from nucleus.

And thus second ionisation energy is more than the first ionization energy of He

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