The helium atom consists of two electrons and a nucleus with charge $Z=2$. The contribution to the potential energy due to the attraction from the nucleus is $$-\frac{2ke^2}{r_1}-\frac{2ke^2}{r_2},$$ and if we add the repulsion arising from the two interacting electrons, we obtain the potential energy $$V(r_1, r_2)=-\frac{2ke^2}{r_1}-\frac{2ke^2}{r_2}+ \frac{ke^2}{r_{12}},$$ with the electrons separated at a distance $r_{12}=|\boldsymbol{r}_1-\boldsymbol{r}_2|$.