Helium atom
= Helium atom
A neutral <helium atom> contains two <electrons> bound to a <nucleus> of charge $+2e$. Even with a fixed <nucleus> and nonrelativistic kinetics, the repulsion $e^2/(4\pi\epsilon_0r_{12})$ prevents exact separation into two hydrogenic one-electron problems. Its ground configuration is $1s^2$ with total <spin> zero, while distinct occupied orbitals allow both <singlet helium states> and <triplet helium states>.