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Electron Configuration Overview

  • Definition of Electron Configuration:
    • Represents the distribution of electrons in an atom's orbitals.

Electron Configuration of Hydrogen

  • Electron Configuration: One s one ($1s^1$)
    • Electron Count: 1 electron
  • Location:
    • Energy Level: 1
    • Sublevel: s
    • Orbital: $1s$

Electron Configuration of Helium

  • Electron Configuration: One s two ($1s^2$)
  • Electron Count: 2 electrons
    • Reason for Configuration: 1s orbital can hold a maximum of 2 electrons due to the Pauli's exclusion principle.

Aufbau Principle

  • Definition: Electrons fill the lowest available energy orbitals first.
  • Explanation:
    • Electrons will occupy orbitals starting with the lowest energy until filled before moving to the next.
    • Important for determining electron configurations systematically.

Electron Configuration for Lithium and Beryllium

  • Lithium (Li):
    • Electron Count: 3 electrons
    • Configuration: $1s^2 2s^1$
  • Beryllium (Be):
    • Electron Count: 4 electrons
    • Configuration: $1s^2 2s^2$

Pauli Exclusion Principle

  • Definition: No two electrons in an atom can have the same quantum state; specifically, two electrons in the same orbital must have opposite spins.
  • Spin Representation in Diagrams:
    • One electron shown as a half-headed arrow facing up, the other down.

Summary of Electron Configurations for First Elements

  • Boron (B):
    • Electron Count: 5 electrons
    • Configuration: $1s^2 2s^2 2p^1$
    • p Orbital Filling: Electrons can go into any of the three p orbitals, with the convention being to fill them singly first to minimize repulsion.
  • Carbon to Nitrogen:
    • Carbon (C): $1s^2 2s^2 2p^2$
    • Nitrogen (N): $1s^2 2s^2 2p^3$

Noble Gas Notation

  • Purpose: Abbreviates electron configurations for complex atoms to simplify writing and understanding.
  • How to Write:
    1. Identify the noble gas that precedes the element.
    2. Write the noble gas symbol in brackets, followed by the remaining configuration.
  • Example:
    • For lithium, use helium:
    • Configuration:
      • Full: $1s^2 2s^1$
      • Noble Gas: [$He$] $2s^1$

Filling Electron Orbitals for Higher Elements

  • Silicon (Si):
    • Electron Count: 14 electrons
    • Configuration: $1s^2 2s^2 2p^6 3s^2 3p^2$
  • Energy Level Calculation: Ensure total utilized electrons equal the atomic number.

Periodic Table and Electron Configuration

  • Classification of Blocks:
    • s block: contains hydrogen and helium.
    • p block: includes the nonmetals and some metalloids.
    • d block: transition metals.
    • f block: lanthanides and actinides.
  • Trends in Orbital Filling:
    • Transition metals typically involve n-1 d electrons.

Valence Electrons

  • Definition: Electrons in the outermost energy level that participate in chemical bonding.
    • Determine the properties and reactivity of elements.
  • Finding Valence Electrons:
    • Example for phosphorus: Highest occupied energy level is 3, with configuration contributing:
    • $[ ext{Ne}] 3s^2 3p^3$ => 5 valence electrons.

Example of Valence Electron Calculation in Various Elements

  • Sulfur (S):
    • Configuration: $1s^2 2s^2 2p^6 3s^2 3p^4$
    • Valence Electrons: 6
  • Chlorine (Cl):
    • Configuration: $1s^2 2s^2 2p^6 3s^2 3p^5$
    • Valence Electrons: 7

Questions and Practice

  • Practice writing electron configurations and identifying noble gas shorthand for various elements as practice problems.
  • Exam Preparation: Know how to derive both full configurations and shorthand, and understand valence electrons for chemical bonding implications.