What is Hund's Rule of Maximum Multiplicity?
Hund's rule states that for a given electron subshell, electrons will first occupy each orbital singly before any orbital is doubly occupied. Furthermore, all electrons in singly occupied orbitals must have the same spin (a state of maximum multiplicity).
Section 2: The 'Bus Seat' Analogy
A common analogy for Hund's rule is filling seats on a bus. People prefer to take an empty double seat for themselves before they pair up and sit next to someone else. Similarly, electrons 'prefer' to occupy their own orbital within a subshell before pairing up. This arrangement minimizes electron-electron repulsion, leading to a more stable, lower-energy state.
Section 3: A Practical Example with Carbon
Consider the element carbon, which has an electron configuration of 1s²2s²2p². The 2p subshell has three separate orbitals of equal energy (px, py, pz). According to Hund's rule, the two electrons in the 2p subshell will occupy two different orbitals (e.g., one in 2px and one in 2py), both with parallel spins. They do not pair up in the same 2px orbital while the other p-orbitals are empty.
Section 4: Importance in Chemistry
Hund's rule is crucial for correctly predicting the ground-state electron configuration of atoms. This configuration, in turn, determines an element's chemical properties and magnetic behavior. The rule helps explain why certain elements are paramagnetic (attracted to magnetic fields) due to the presence of unpaired electrons, which is a key factor in chemical bonding and reactivity.