Electron Configuration

Configuration Principles

  • Aufbau Principle: Dictates that electrons fill orbitals from lower to higher energy levels (1s, 2s, 2p, 3s, etc.).

  • Hund's Rule: Electrons fill each orbital singly before pairing, all unpaired electrons must have the same spin to maximize total spin.

  • Pauli Exclusion Principle: No two electrons in an atom can have the same set of four quantum numbers. Each orbital can hold a maximum of two electrons with opposite spins.

Lesson Objectives

  • Content: Understand electron configuration, including:

    • The Aufbau Principle

    • Hund’s Rule

    • Pauli Exclusion Principle

  • Learning Objectives:

    • Describe arrangement of atomic orbitals (s, p, d, f) and their maximum capacities.

    • Demonstrate understanding of principles governing electron configurations.

    • Write complete and shorthand electron configurations for atoms.

Electron Configuration Overview

  • What are Electron Configurations?

    • Arrangement of electrons around the atomic nucleus in energy levels.

    • Describes electron distribution in atomic orbitals.

    • Shorthand representation of electron arrangement in orbitals, levels, and sublevels.

Understanding Electron Configuration

  • Notation Example:

    • 1s² represents:

      • Main energy level (1)

      • Type of orbital (s)

      • Number of electrons (2)

    • Electron configurations are written sequentially based on increasing energy.

Aufbau Principle Details

  • Order of filling energy levels: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p.

  • Sublevels and Capacities:

    • s: 2 electrons

    • p: 6 electrons

    • d: 10 electrons

    • f: 14 electrons

  • Remember: Distribution should not exceed designated maximum electrons per sublevel.

Hund's Rule of Maximum Multiplicity

  • Describes the filling order of electrons in orbitals of a subshell.

  • Electrons fill orbitals singly first, maximizing spin.

  • Correct Method: E.g., 1s² 2s² 2p²

  • Incorrect Method: Pairing electrons in multiple orbitals before all have one electron (e.g., 1s² 2s² 2p2 1s² 2s² 2p3)

Magnetic Properties

  • Diamagnetic: Atoms with paired electrons, net spin is zero.

  • Paramagnetic: Atoms with unpaired electrons, yielding a non-zero net spin.

Pauli Exclusion Principle

  • Maximum of two electrons per orbital with opposite spins.

  • Fundamental Rule: No two electrons in the same atom can have the same values for all four quantum numbers.

Steps in Writing Electron Configurations

  1. Identify the element and atomic number from the periodic table.

  2. Use the electron configuration mnemonic for reference.

  3. Ensure all orbitals are filled except for the last one, which may only contain the maximum number of electrons if noble gas.

  4. Verify that the sum of the exponents equals the total number of electrons.

Examples of Writing Electron Configurations

  • Aluminum (Al, Atomic Number 13):

    • Complete Configuration: 1s² 2s² 2p⁶ 3s² 3p¹

    • Shorthand Configuration: [Ne] 3s² 3p¹

  • Fluorine (F, Atomic Number 9):

    • Complete Configuration: 1s² 2s² 2p⁵

    • Shorthand Configuration: [He] 2s² 2p⁵

  • Magnesium (Mg, Atomic Number 12):

    • Complete Configuration: 1s² 2s² 2p⁶ 3s²

    • Shorthand Configuration: [Ne] 3s²

Practice Activity

  • Task: Write complete and shorthand electron configurations for provided elements.