Study Notes on Electron Configuration and Orbital Filling

Electronic Configuration of Elements

Overview of Electron Configuration

  • Electron Configuration: A method to describe the arrangement of electrons in an atom's orbitals.

    • Electrons fill atomic orbitals starting from the lowest energy before moving to higher energy levels (Aufbau principle).

Basic Principles of Electron Configuration

  • Order of Filling Orbitals:

    • Lowest to highest energy.

    • 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s

    • Key to remember the order of orbitals: each subshell can hold a maximum number of electrons (e.g., s=2, p=6, d=10).

Filling Orbitals Example

  • Helium (He):

    • Electron configuration: 1s².

  • Fluorine (F):

    • Electron configuration: 1s² 2s² 2p⁵.

  • Neon (Ne):

    • Total electrons in neon: 10

    • Electron configuration: 1s² 2s² 2p⁶.

Example of Chlorine

  • Chlorine (Cl) Electron Configuration:

    • Request to write configuration in notebook.

    • Answer should be structured as follows:

    • 1s² 2s² 2p⁶ 3s² 3p⁵.

    • Focus on understanding the order of orbitals filled and knowing the immediate past noble gas configuration.

Understanding Orbital Filling and Stability

  • Filling up of orbitals leads to stability in electron arrangement. When orbitals are filled:

    • Elements do not easily donate or accept electrons during compound formation.

    • These elements are considered noble and are unreactive.

Filling Out Electron Configuration

  • Example for Transition Elements:

    • Group classification from 3B to 8B corresponds to the transition elements.

    • Transition metals have varying charges, leading to different common oxidation states.

Special Considerations in Orbital Filling

  • Hybridization & Anomalies:

    • Certain elements like chromium (4 Cr) and molybdenum (4 Mo) display irregular electron fillings due to stability preferences:

    • Instead of filling 4s completely, one electron moves to the 3d orbital to achieve a half-filled d subshell, which is more stable:

      • Chromium: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵

      • Molybdenum: Adjust electrons accordingly to achieve half-filled configuration.

Periodic Table Relationships

  • Position in Periodic Table:

    • Understand that the periodic table's structure helps identify the electron configurations quickly.

    • Starting from noble gases (like krypton (Kr)), filling continues through 5s², then 4d¹⁰ for elements in successive periods.

Electron Configuration Guidelines

  • When writing configurations, note the following:

    • s orbitals fill first, followed by p, then d (which is always one less than the period number).

    • f orbitals fill only after the preceding d subshell.

  • Example for Rhodium:

    • Difficulties arise during configurations, especially for transition metals with partially filled orbitals.

Summary of Electron Configuration Notation

  • Write the configurations correctly and understand exceptions to normal filling rules.

  • Use noble gas core shorthand for efficiency, e.g.,: [Ne] 3s² 3p⁵ for Chlorine or [Kr] to denote configurations involving noble gases.