Now explaining the second rule, if it speaks technically, the first electron in a sublevel could be either spin up or spin down. To understand this we can visualise the process of electrons which exhibit the same behaviour as the same poles of a magnet would if they come into contact, as negatively charged electrons filled orbitals, the first try to get as far as possible from each other before having to better.Įlectrons are negatively charged because of which they ripple each other, so we see that electrons tend to minimise repulsion by first occupying their own orbitals rather than sharing an orbital with another electron now according to quantum mechanical calculations it is shown that the electrons in singly occupied orbitals are less effectively screened or shielded from the nucleus, which can be called as electron shielding. Add the ground states atoms tend to have a huge number of unpaired electrons.

When the electrons are assigned to the orbital is, similar energy is required by N electron to fill or the orbital is, which is also referred to as degenerate orbitals, this is before pairing with another electron in a half an orbital. To maximise the total spin of the electron, all of the electrons in singly occupied orbitals have the same spin. Now Hund’s rule states that every orbit in a sub-level is occupied singly before any orbit is doubly occupied. In Aufbau’s principle section, we discuss how the electrons fill the lowest energy orbital first and then move up to higher energy orbital is only after they have filled the lower energy orbitals when we look at it from a very deep perspective we can figure out that the 1s orbitals should technically get filled before the 2s orbital because of the lower value that 1s orbital has which in turn gives it lower energy so from this theory, where we see a problem with think of a solution and provide an answer to this question which involves Hund’s rule. First, we will look into Aufbau’s rule, understand it and then go to Hund’s rule. There are multiple rules which we need to understand before we actually go on explaining Hund’s rule.

Aufbau principle diagram pdf