Chemistry Essentials: Hund’s Rule and Electron Configuration

by Yuvi K - December 17, 2023

What is Chemistry Essentials : Hund’s Rule and Electron Configuration ?

Chemistry essentials related to Hund’s Rule and electron configuration are important topics covered by chemistry courses and exams. In chemistry, Hund’s rule is the principle that states that whenever an atom has more than one electron in a given subshell, the electrons will fill each sublevel one by one and remain unpaired until each sublevel has one electron before pairing up.

Electron Configuration is the arrangement of electrons in an atom or molecule. The electrons are arranged into shells and subshells according to their energy levels — the lower the energy level, the farther out from the nucleus of the atom the electrons can be found.

Overview of Hund’s Rule & Electron Configuration

In the theory of molecular structure, Hund’s rule (named after the German physicist Friedrich Hund) states that in a set of degenerate orbitals, electrons will occupy different orbitals with the same spin (also known as parallel spins) rather than pairing up to fill the lowest-energy orbital. This rule is important in chemistry since it helps explain why molecules exist in certain shapes and configurations.

Electron configuration is the arrangement of electrons in an atom or molecule. The electrons are arranged into shells and subshells according to their energy levels — the lower the energy level, the farther out from the nucleus of the atom the electrons can be found. An atom’s electron configuration is important for understanding its chemical properties and reactivity.

Hund’s Rule & Electron Configuration : Explanation in detail

Hund’s Rule states that when multiple orbitals of the same energy level are available and no two electrons may occupy the same orbital, each orbital of that energy level will contain one electron until all orbitals of that energy level are occupied before any pairing occurs.

This rule ensures that each orbital is filled with one electron moving in one direction before two electrons of the opposite spin move into that orbital. Thus, electrons fill orbitals in a manner such that each orbital has a single electron before any orbital is filled with two electrons.

When filling in electrons, the Aufbau Principle is followed. According to the Aufbau Principle, electrons fill up orbitals in order of increasing energy. This means that electrons will fill lower-energy orbitals before filling higher-energy orbitals.

Hund’s Rule and Electron Configuration Examples

Hund’s Rule can be famously demonstrated by the electron configuration of oxygen:

In this example, the lowest-energy orbitals (1st shell) are filled with two electrons, followed by the eight electrons filling up the second shell (note that each subshell is still holding one electron). The remaining six electrons are then placed unpaired into the third shell.

Now, let us look an example of electron configuration. Consider calcium, an element with atomic number 20:

In this example, the lowest-energy orbitals (1st shell) are filled with two electrons, followed by the 8 electrons filling up the second shell. The remaining 8 electrons are then placed into two subshells with 4 electrons in each in order to adhere to the Hund’s rule.

Conclusion

Hund’s Rule and Electron Configuration are important concepts in chemistry and understanding them is essential for any student studying this field.

Together, these rules explain why atoms exist in certain shapes and configurations which in turn, explains why some reactions occur and others don’t. With a thorough understanding of these concepts, chemists are able to predict the behavior of atoms and create new and exciting reactions.