# How do you calculate the ionization energy of He+?

${R}_{H} = \Delta {H}_{I E} \left(\text{H}\right)$
$=$ $\text{13.61 eV}$
$= \Delta {H}_{I E} \left({\text{He}}^{+}\right)$
Why can I say this? How many electrons does ${\text{He}}^{+}$ have?