Question

Describe Hund's rule of maximum multiplicity.

Short answer

Hund's rule, named after Friedrich Hund, states that every orbital in a subshell will be singly occupied with one electron before any is doubly occupied, and all electrons in singly occupied orbitals have the same spin, thus ensuring that the atom is in its lowest possible energy state. For instance, for a carbon atom, the two electrons in the 2p shell will each occupy a different 2p orbital, adhering to Hund's Rule.

Step-by-step solution

Understanding Hund's Rule

Hund's rule, named after Friedrich Hund, is an observation in atomic theory which states that every orbital in a subshell is singly occupied with one electron before any one orbital is doubly occupied, and all electrons in singly occupied orbitals have the same spin. This is also referred to as the Rule of Maximum Multiplicity.

Dividing Hund's Rule into Parts

Hund's rule can be broken down into three parts: 1. Electrons will always attempt to enter an empty orbital before they pair up. 2. All unpaired electrons must have the same spin (usually, but not always, spin-up). 3. The total spin of the electrons in an atom with a partially filled sub-shell is maximum, ensuring the atom is in the lowest possible energy state.

Providing an Example

Let's take the example of carbon atom (atomic number 6). The electronic configuration will be \(1s^{2} 2s^{2} 2p^{2}\). In the 2p shell, there are three orbitals and two electrons. As per Hund's rule, each electron will occupy the p orbitals singly before doubling up. So, the two electrons in the 2p shell will each occupy a different 2p orbital, keeping the atom in its lowest possible energy state.

Key concepts

Atomic Theory

Atomic theory is a scientific framework that helps us understand the nature of matter. It explores how atoms form the building blocks of every element and molecule. At the heart of atomic theory is the concept of the atom: a small, densely packed unit that consists of a nucleus surrounded by a cloud of electrons.
These electrons exist in regions of space called orbitals, which are governed by principles like those outlined in Hund's rule. Hund's rule is part of a larger set of rules and observations that dictate how electrons behave around the nucleus. This rule helps describe electron arrangements and ultimately influences the atom's properties.
Atomic theory thus provides the foundation for understanding the complex behavior of electrons, which in turn shapes the chemical properties of the atom and determines how different atoms interact with each other in chemical reactions.

Electron Configuration

Electron configuration describes the distribution of electrons in an atom's orbitals. Each electron inhabits an energy level, represented by shells and subshells in the electronic structure of an atom. A proper understanding of electron configuration is crucial for applying Hund's rule effectively.
The configuration is typically written in a compact form, such as for carbon: \(1s^{2} 2s^{2} 2p^{2}\). This notation specifies that carbon has two electrons in its 1s orbital, two in its 2s orbital, and two more in its 2p orbitals.
Hund's rule fits within electron configuration by dictating how electrons fill these subshells to minimize repulsion and achieve stability. This rule ensures that electrons will first occupy empty orbitals within a subshell before pairing up, optimizing the atom's energy state.

• Ensures energy minimization
• Dictates filling order
• Supports the concept of electron spin

Orbitals

Orbitals are regions around an atom's nucleus where electrons are most likely to be found. They form specific patterns or shapes—such as s, p, d, and f—that are determined by the energy level and angular momentum of the electron.
Hund's rule plays a crucial role in determining how electrons populate these orbitals. For example, in the case of the 2p subshell of carbon, each available orbital is filled singly before any electron pairing occurs. This arrangement minimizes electron repulsion within the atom.
By understanding orbitals, we gain insight into the distribution of electrons and how this affects the overall behavior of the atom in chemical reactions and bonding. Orbitals not only define where electrons are likely to be found but also help us visualize the spatial distribution of electron density.

Electron Spin

Electron spin is a quantum property of electrons, which describes their intrinsic angular momentum. This property can manifest as either "spin-up" or "spin-down," typically represented as \(+\) or \(-\).
Hund's rule of maximum multiplicity specifically emphasizes the importance of electron spin when occupying orbitals. For instance, electrons in singly occupied orbitals should have parallel spins, which helps lower the system's total energy. This arrangement creates the lowest possible energy state for the atom.
Understanding electron spin is critical for predicting the magnetic properties of an atom. Atoms with unpaired electrons often feature unbalanced spin states, which can lead to magnetism. Consequently, electron spin not only informs us about the stability of an atom but also its interactions with magnetic fields.

Energy States

Energy states describe the potential energy configurations that an atom or a group of electrons can possess. Transitioning between these states involves absorbing or releasing energy.
Hund's rule is instrumental in achieving the lowest energy state possible. By maximizing the number of unpaired electrons with parallel spins, the energy repulsion between electrons is reduced, lowering the energy state of the atom. This is crucial for electron configuration stability.
Atoms naturally seek the lowest energy state, as it is most stable. The alignment of electrons under Hund's rule helps achieve this stability, impacting the chemical reactivity and interactions of the atom.

• Influences reactivity and stability
• Defines electronic interactions

Understanding energy states provides insight into how atoms maintain low-energy configurations and how they might behave when subjected to external forces or during chemical reactions.