Electron pairsIn most cases in the outer electron shell of a (non) charged ion 8 electrons are present.
The case with only 2 electrons in the smallest ions is not considered here.
The electrons repel each other due to their negative charge. That is why can be expected,
they take positions as far away as possible from each other in a electron shell,
being at the vertices of a cube.
However, about a century ago Gilbert Lewis developed the theory,
the 8 electrons would dwell as pairs in the 4 vertices of a tetraeder.
Electron pairs, most of the cases displayed as a hyphen, are important
for the organic chemical bonds in molecules.
It is to be expected, the electrons possess more electrical energy in state 2
than in state 1, provided that the ion exists in free state.
However, in case of a bond state 2 has nevertheless a lesser energy.
The two electrons in a pair always have opposite spins (↑↓)