Lexico Unisciel english version

The Hund's rules able us to define the orbitals occupation and the spin state at the ground state. The first rule says that as many orbitals as possible have to be used in a subshell. Thus we take the electronic repulsion in account, by positioning the electrons on as many levels as possible to minimize their mutual repulsion : electrons repulse each other less if there are on different orbitals. The second rule states that the configurations with the highest number of parallel spins are the favoured ones. It explains the influence of exchange energy.