Overview
This lecture reviews how to write electron configurations for elements, covering energy levels, sublevels, and the rules that govern electron arrangement.
Electron Configuration Basics
- Electron configuration describes how electrons are arranged in energy levels around an atom's nucleus.
- The configuration uses numbers (principal quantum numbers), letters (orbital/sublevel types), and superscripts (number of electrons in each sublevel).
- Sublevel letters: s (sharp), p (principal), d (diffuse), f (fundamental).
Maximum Electrons per Sublevel
- s sublevel can hold up to 2 electrons.
- p sublevel can hold up to 6 electrons.
- d sublevel can hold up to 10 electrons.
- f sublevel can hold up to 14 electrons.
Steps for Writing Electron Configuration
- Identify the element's atomic number from the periodic table.
- Use correct order of sublevels, often with the help of a mnemonic or diagonal rule for arrangement.
- Write out the configuration according to energy levels and sublevels.
Principles Governing Electron Arrangement
- Aufbau Principle: Electrons fill the lowest energy orbitals first before filling higher ones.
- Pauli Exclusion Principle: A maximum of 2 electrons can occupy an orbital, and they must have opposite spins.
- Hund's Rule: Electrons fill degenerate (equal energy) orbitals singly first, with parallel spins, before pairing.
Example Electron Configurations
- Phosphorus (Atomic number 15): 1s² 2s² 2p⁶ 3s² 3p³
- Oxygen (Atomic number 8): 1s² 2s² 2p⁴
Key Terms & Definitions
- Electron Configuration — Shorthand notation showing how electrons are arranged in an atom.
- Orbital — A region around the nucleus where electrons are likely to be found.
- Sublevel — Division of energy levels in an atom (s, p, d, f).
- Aufbau Principle — Rule stating electrons occupy lowest energy orbitals first.
- Pauli Exclusion Principle — Rule stating no two electrons in an atom can have the same set of quantum numbers.
- Hund's Rule — Rule stating electrons fill orbitals singly before pairing.
Action Items / Next Steps
- Practice writing electron configurations for different elements.
- Read about quantum numbers to prepare for the next topic.