Apartment Rules Electron Rules From the Bottom Up: Rooms must be filled from Aufbau Principle: the electrons fill the available the ground floor up. Fill the one room on the first orbitals from lowest energy to highest energy. In the floor before starting to put new tenants on the ground state all the electrons are in the lowest second floor. Then fill the s room before the p possible energy level. rooms. At higher floors the order might change a bit. Singles the owner of the building wants to Hund’s Rule: The electrons must be placed into have the tenants spread out as much as possible. the orbitals in such a way that no are put For that reason singles are placed in rooms before together unless absolutely necessary. That is, couples. If couples must be placed into a room then single electrons must be placed into boxes first and all of the other rooms on that floor must already then paired up if necessary. have a single in them. Opposite Gender Only: When two people are Pauli Exclusion Principle: Electrons come in two placed in a room they must be of opposite genders. varieties based on the direction they are ‘spinning’. No men may room together and no women may There is an Up spin and a Down spin. Up and room together. This is an arbitrary rule on the part Down spins are always paired together and Up-Up of the owners: in a just world we wouldn’t have to or Down-Down combinations are not allowed. No follow it. But quantum mechanics has nothing to do two electrons can ever be in the same place at the with justice. same time.
Apartment Rules Electron Rules From the Bottom Up: Rooms must be filled from the ground floor up. Fill the one room on the first floor before starting to put new tenants on the second floor. Then fill the s room before the p rooms. At higher floors the order might change a bit. Aufbau Principle: the electrons fill the available orbitals from lowest energy to highest energy. In the ground state all the electrons are in the lowest possible energy level. Singles the owner of the building wants to have the tenants spread out as much as possible. For that reason singles are placed in rooms before couples. If couples must be placed into a room then all of the other rooms on that floor must already have a single in them. Hund’s Rule: The electrons must be placed into the orbitals in such a way that no are put together unless absolutely necessary. That is, single electrons must be placed into boxes first and then paired up if necessary. Opposite Gender Only: When two people are placed in a room they must be of opposite genders. No men may room together and no women may room together. This is an arbitrary rule on the part of the owners: in a just world we wouldn’t have to follow it. But quantum mechanics has nothing to do with justice. Pauli Exclusion Principle: Electrons come in two varieties based on the direction they are ‘spinning’. There is an Up spin and a Down spin. Up and Down spins are always paired together and Up-Up or Down-Down combinations are not allowed. No two electrons can ever be in the same place at the same time.