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Ionization Enthalpy in Periodic Properties

Jul 30, 2024

Class 11 Chemistry - Classification of Elements and Periodic Properties - Ionization Enthalpy

Overview

  • Importance of Isoelectronic Species: Crucial for competitive exams (JE, NEET, CET).
  • Todays Topic: Ionization Enthalpy (IE), also known as Ionization Potential or Ionization Energy.
  • Definition: Energy required to remove the outermost electron from a neutral gaseous atom in its ground state.

Key Concepts

Ionization Enthalpy (IE)

  • Various Terms: Ionization Enthalpy, Ionization Energy, Ionization Potential are synonymous.
  • Definition: Energy required to remove the last electron from the valence shell of a neutral gaseous atom in its ground state.
  • Condition: The atom must be isolated (single), in gaseous state, and in its ground state.
  • Unit: kJ/mol (kilojoule per mole)

Successive Ionization Enthalpies

  • Process: Removal of electrons one by one, not simultaneously.
  • Example with Aluminium: Al → Al⁺ (IE1), Al⁺ → Al²⁺ (IE2), Al²⁺ → Al³⁺ (IE3).
  • Trend: IE3 > IE2 > IE1.
  • Reason: Inner electrons have stronger attraction to the nucleus; more energy required to remove.

Factors Affecting Ionization Enthalpy

  1. Atomic Size: Inverse Relationship
    • Larger Atomic Size → Smaller IE.
    • Smaller Atomic Size → Larger IE.
  2. Nuclear Charge: Direct Relationship
    • Larger Nuclear Charge → Larger IE.
    • Positive charge of nucleus (protons) attracts electrons more strongly.
  3. Shielding/Screening Effect: Inverse Relationship
    • Inner electrons screen/shield outer electrons from nucleus attraction.
    • Higher Screening → Lower IE.
    • Screening Effect in order: s > p > d > f
  4. Penetrating Power: Placement of Electrons
    • Electrons in s-orbital are hard to remove (high IE) due to their proximity to nucleus.
    • Order of ease to remove: s < p < d < f
  5. Electronic Configuration: Stability Matters
    • Stable configurations (fully filled/half-filled): higher IE.
    • Example: N (1s² 2s² 2p³) has higher IE than O (1s² 2s² 2p⁴).

Variation of Ionization Enthalpy

Across a Period

  • From left to right, IE increases.
  • Reason: Decreasing atomic size, increasing nuclear charge.
  • Exceptions: 2nd group elements have higher IE than 13th group due to stability (e.g., Beryllium vs. Boron). Similar exception in 15th (e.g., Nitrogen) and 16th group elements.

Down a Group

  • From top to bottom, IE decreases.
  • Reason: Increasing atomic size means outer electrons are further from nucleus, thus less attraction.
  • Notable Element: Cesium has the lowest IE.
  • Noble Gases: Have the highest IE due to stable configurations.

Summary

  • Ionization Enthalpy: Key measure for predicting chemical behavior and properties like oxidizing/reducing nature, metallic/non-metallic character, etc.
  • Factors: Atomic size, nuclear charge, screening effect, penetrating power, and electronic configuration significantly influence IE.
  • Trends: IE trends across periods and down groups have predictable patterns with notable exceptions.

Next Topic

  • Upcoming: Electron gain enthalpy (Electron Affinity).

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Full transcript