Summary
Highlights
This video lecture serves as a recap on writing electron configurations and preparation for understanding quantum numbers. Electron configuration describes the arrangement of electrons in energy levels, orbitals, and sub-levels, using numbers, letters, and superscripts.
The number in electron configuration represents the principal quantum number or energy level. Letters (s, p, d, f) denote different orbitals or sub-levels: s for sharp, p for principal, d for diffuse, and f for fundamental. Superscripts indicate the number of electrons in a specific sub-level.
Each sub-level has a maximum electron capacity: s-sub-level holds 2 electrons, p-sub-level holds 6, d-sub-level holds 10, and f-sub-level holds 14.
The first step is to determine the atomic number of the element using the periodic table. The atomic number is usually found in the upper portion of the element symbol.
The second step uses an electron configuration mnemonic device to determine the proper arrangement of energy sub-levels. Three principles guide electron configuration: Aufbau principle, Pauli's Exclusion Principle, and Hund's Rule.
The Aufbau principle (German for 'built up') states that electrons first fill orbitals of the lowest energy before occupying higher energy orbitals.
Pauli's Exclusion Principle states that no more than two electrons in an atom can occupy an orbital, and if two electrons are in the same orbital, they must have opposite spins. Paired electrons have opposite spins, while unpaired electrons are single in an orbital.
Hund's Rule states that for a set of orbitals with equal energy, electrons will individually occupy each orbital with parallel spins before any orbital is doubly occupied. This rule helps determine if an atom is paramagnetic (attracted to magnetic fields due to unpaired electrons) or diamagnetic (not attracted due to all paired electrons).
The sum of the superscripts, representing the number of electrons in each sub-level, must equal the atomic number of the element. An example of Phosphorus (atomic number 15) is used to demonstrate writing its electron configuration.
A summary of the video lecture reiterates that electron configuration is a shorthand representation of electron arrangement. It reviews the maximum electron capacities of s, p, d, and f sub-levels, and the number of orbitals each possesses. The three principles—Aufbau, Pauli's Exclusion, and Hund's Rule—are briefly restated. The instructor then works through an example for oxygen.