# Homework Help: Calculating second ionization energy of He

1. Sep 12, 2012

### BobRoss

1. The problem statement, all variables and given/known data

The equation En=-Z2RH/n2 gives the energy (according to the Bohr model) of the energy levels available to an electron in any hydrogen-like atom. Calculate the second ionization energy of He(in J). The second ionization energy of He is the ionization energy of He+.

2. Relevant equations

En=-Z2RH/n2 where RH=2.178x10-18J

Z=2
n=?

3. The attempt at a solution

I don't understand which value I am supposed to use for n. When I look up the second ionization energy of He I find that the answer is 54.4 eV or 8.712x10-18J, which is the answer I get when I input n=1 into the above equation. But it's asking for the second ionization energy of He, so why would I use n=1?

2. Sep 13, 2012

### AGNuke

n=1 is the orbit number of He. He has configuration of 1s2, meaning that both 2 electrons are in 1st orbit. 2nd Ionization energy refers to removal of 2nd electron, or removal of only electron of He+ ion, in this case.

Z refers to the atomic number of the species. For He, Z = 2.

3. Jul 18, 2013

### knowLittle

Thanks for the question.