Electronic Configuration

Electronic Configuration

Key Notes:

Introduction

  • Electronic Configuration refers to the arrangement of electrons in the orbitals of an atom.
  • It follows specific rules and principles that govern the distribution of electrons in different energy levels, sublevels, and orbitals.

Key Concepts

  1. Energy Levels (Shells):
    • Represented by the Principal Quantum Number (nn).
    • Examples: n=1,2,3,…
  2. Sublevels (Subshells):
    • Each energy level has sublevels (s,p,d,f).
    • Each sublevel has specific orbitals:
      • s: 1 orbital (2 electrons).
      • p: 3 orbitals (6 electrons).
      • d: 5 orbitals (10 electrons).
      • f: 7 orbitals (14 electrons).
  3. Orbitals:
    • Regions around the nucleus where electrons are most likely found.
    • Each orbital can hold 2 electrons with opposite spins.

Rules for Writing Electronic Configuration

  1. Aufbau Principle:
    • Electrons fill orbitals in order of increasing energy.
    • Energy order: 1s<2s<2p<3s<3p<4s<3d<4p…
  2. Pauli Exclusion Principle:
    • No two electrons in an atom can have the same set of all four quantum numbers.
    • Each orbital can hold a maximum of 2 electrons with opposite spins.
  3. Hund’s Rule:
    • Electrons occupy degenerate orbitals (orbitals of the same energy) singly first, before pairing.

Notation

  1. Standard Notation:
    • Represented as nlⁿᵘᵐᵇᵉʳ ᵒᶠ ᵉˡᵉᶜᵗʳᵒⁿˢ.
    • Example: 1s²2s² 2p⁶.
  2. Orbital Diagram:
    • Uses arrows to show electron spins.
    • Example:
      1s ↑↓, 2s ↑↓, 2p ↑ ↑ ↑

Examples of Electronic Configurations

  1. Hydrogen (Z=1Z = 1): 1s¹.
  2. Helium (Z=2Z = 2): 1s².
  3. Carbon (Z=6Z = 6): 1s² 2s² 2p²s
  4. Neon (Z=10Z = 10): 1s²2s² 2p⁶

Electronic Configuration of Elements in the Periodic Table

  • Groups: Elements in the same group have similar outermost configurations.
    • Example: Group 1: ns¹.
  • Periods: Elements in the same period have the same number of energy levels.

Shortcut Notation (Noble Gas Configuration)

  • For elements with many electrons, configurations can be abbreviated using noble gases:
    • Example: Sodium (Z=11): [Ne] 3s¹.

Importance of Electronic Configuration

  1. Chemical Properties:
    • Determines reactivity, valency, and bonding.
  2. Periodic Trends:
    • Explains trends like atomic size, ionization energy, and electronegativity.
  3. Stability:
    • Atoms with fully filled or half-filled orbitals are more stable.

Let’s practice!