Page "Helium" Paragraph 22

In the perspective of quantum mechanics, helium is the second simplest atom to model, following the hydrogen atom.

Helium is composed of two electrons in atomic orbitals surrounding a nucleus containing two protons along with some neutrons.

As in Newtonian mechanics, no system consisting of more than two particles can be solved with an exact analytical mathematical approach ( see 3-body problem ) and helium is no exception.

Thus, numerical mathematical methods are required, even to solve the system of one nucleus and two electrons.

Such computational chemistry methods have been used to create a quantum mechanical picture of helium electron binding which is accurate to within < 2 % of the correct value, in a few computational steps.

In such models it is found that each electron in helium partly screens the nucleus from the other, so that the effective nuclear charge Z which each electron sees, is about 1. 69 units, not the 2 charges of a classic " bare " helium nucleus.