Hund’s rule

Oct 31, 2023

Electron configuration, the arrangement of electrons within an atom, is a fundamental concept in chemistry. Among the principles governing this arrangement, Hund’s Rule stands out as a crucial guide, shedding light on the order and orientation in which electrons fill atomic orbitals. In this article, we will delve into the intriguing world of Hund’s Rule, exploring its significance and providing an informative table that summarizes its key aspects.

The Essence of Hund’s Rule

Hund’s Rule, named after the German physicist Friedrich Hund, is a principle that helps us understand how electrons populate different atomic orbitals. It is particularly relevant when we encounter degenerate orbitals, which are orbitals of the same energy level but different spatial orientations. Hund’s Rule can be summarized as follows:

Electrons occupy degenerate orbitals singly before pairing up.

This rule has profound implications for electron configuration, helping to elucidate the fascinating world of atomic structure.

Understanding Hund’s Rule in Action

To better grasp Hund’s Rule, let’s consider the example of the carbon atom (atomic number 6) and its electron configuration. Carbon has six electrons to distribute among its orbitals.

In the carbon atom, there are two possible energy levels: the 1s orbital and the 2s and 2p orbitals. Following Hund’s Rule, electrons will fill these orbitals as follows:

  • The first two electrons will occupy the 1s orbital, each with opposite spins, denoted as ↑ and ↓. This results in a completely filled 1s orbital.
  • The next two electrons will go to the 2s orbital, again with opposite spins (↑ and ↓), resulting in a filled 2s orbital.
  • The final two electrons will be distributed among the 2p orbitals. According to Hund’s Rule, they will enter separate 2p orbitals, each with an ‘up’ (↑) spin, until all the orbitals have one electron. Only then will the electrons in the 2p orbitals begin to pair up with opposite spins.

This arrangement aligns with Hund’s Rule, which ensures that electrons occupy different degenerate orbitals singly (with the same spin) before pairing up. It maximizes the repulsion between electrons and stabilizes the atom.

A Handy Table to Summarize Hund’s Rule

Here’s a handy table to encapsulate the key aspects of Hund’s Rule for easy reference:

Hund’s Rule: Electrons in Degenerate Orbitals
1. Electrons occupy degenerate (same-energy) orbitals one by one, rather than pairing up.
2. When electrons fill degenerate orbitals, they have the same spin (↑) before any orbital receives a second electron with opposite spin (↓).
3. The occupation of degenerate orbitals singly before pairing up minimizes electron-electron repulsion, increasing stability.

Hund’s Rule is instrumental in determining electron configuration not only for carbon but for all elements in the periodic table. It provides insight into the behavior of electrons, helping chemists and physicists unlock the secrets of matter’s structure and properties.

In conclusion, Hund’s Rule is a cornerstone of electron configuration, guiding the filling of degenerate orbitals in a manner that minimizes repulsion and maximizes stability. This fundamental principle is indispensable in our quest to comprehend the intricacies of the atomic world.

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