Question

Energy of $24.6\text{eV}$ is required to remove one of the electrons from a neutral helium atom. The energy in $\left(\text{eV}\right)$ required to remove both the electrons from a neutral helium atom is

Answer 1

When one of the electrons is removed from a neutral helium atom, energy is given by $E_n.$
$E_n=-\frac{13.6Z^2}{n^2}$ eV per atom
For helium ion, Z = 2, when double ionised.
For first orbit, n = 1
$\therefore E_1=-\frac{13.6}{(1{)}^2}\times (2{)}^2=-54.4\text{eV}$
$\therefore$ Energy required to liberate second electron from helium $54.4\text{eV}$
$\therefore$ Total energy required or energy required to remove both the electrons from helium $=E_1+E_2$
$=(54.4+24.6)\text{eV}=79\text{eV}.$