Overview
This lecture reviews electron configuration, introduces the Aufbau principle, and explains how to use it for determining the placement of electrons in atoms, especially beyond calcium.
Electron Configuration Basics
- Orbitals are regions in atoms where electrons are likely to be found, organized into shells and subshells.
- Electron configuration describes how electrons are distributed among an atom’s orbitals.
- The order of filling orbitals generally follows increasing energy levels (e.g., 1s, 2s, 2p).
Using the Aufbau Principle
- The Aufbau principle (German for "building up") dictates the order electrons fill orbitals: start from lowest to highest energy.
- Neon (atomic number 10): configuration is 1s² 2s² 2p⁶.
- Argon (atomic number 18): configuration can be written as [Ne] 3s² 3p⁶.
- Calcium (atomic number 20): configuration is [Ar] 4s², skipping filling the 3d subshell first.
- Scandium (atomic number 21): configuration is [Ar] 4s² 3d¹.
Order of Filling Subshells
- Typical filling order: 1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s, etc.
- Sometimes, actual energy considerations can shift the order (especially with transition metals).
Periodic Table Blocks
- S block: first two columns and helium, where s subshells fill.
- P block: spans the six rightmost columns, where p subshells fill.
- D block: central block (transition metals), where d subshells fill.
Key Terms & Definitions
- Orbital — region in an atom where an electron is likely to be found.
- Electron Configuration — the arrangement of electrons in atomic orbitals.
- Aufbau Principle — method for determining the order electrons fill atomic subshells (lowest energy first).
- Subshell (s, p, d, f) — divisions within electron shells, each with specific shapes and capacities.
- Periodic Table Blocks — s, p, d blocks correspond to the subshell being filled.
Action Items / Next Steps
- Practice writing electron configurations for elements beyond calcium.
- Review periodic table blocks: identify which elements belong to s, p, and d blocks.