Lecture Notes: Trends in the Periodic Table

Overview

• Main Focus: Understanding trends in the periodic table related to:
  • Ionization energy
  • Atomic and ionic radii
  • Electron affinity
  • Electronegativity
• Key Concept: Coulomb's Law
  • Force between two charged particles is proportional to the product of their charges divided by the square of the distance between them.

Coulomb's Law and Effective Nuclear Charge (Zᵉᶠᶠ)

• Coulomb's Law applies to periodic table trends:
  • Q1: Effective positive charge from protons (nucleus)
  • Q2: Charge of an electron
• Zᵉᶠᶠ (Effective Nuclear Charge)
  • Calculated as atomic number minus shielding (core electrons)
  • Valence Electrons: Key focus due to being the outermost shell and determining reactivity

Trends in the Periodic Table

Effective Nuclear Charge

• Group 1 Elements: Effective charge of ~1
  • Ex: Hydrogen (atomic number 1, no core electrons)
• Halogens: Effective charge ~7
  • Ex: Fluorine (atomic number 9, 2 core electrons)
• Noble Gases: Generally high effective charge
  • Ex: Helium (effective charge of 2), Neon (effective charge of 8)

Atomic Radius

• Left to Right: Radius decreases within a period
• Top to Bottom: Radius increases within a group
• Overall Trend: Radius decreases up and to the right of the periodic table

Ionization Energy

• Definition: Energy required to remove an electron from an atom
• High Ionization Energy: Top right of the periodic table
  • Noble gases and halogens especially
• Low Ionization Energy: Bottom left (e.g., Francium)

Electron Affinity

• Definition: Energy change when an electron is added to an atom
• High Electron Affinity: Top right, especially halogens
• Low Electron Affinity: Bottom left
• Note: Convention may refer to high electron affinity as releasing more energy (negative electron affinity)

Electronegativity

• Definition: Tendency of an atom to attract shared electrons in a bond
• Correlation: Strongly correlated with electron affinity
• Measurement: Less clear-cut than electron affinity

Conclusion

• Coulomb's Law and effective nuclear charge help explain periodic trends
• Understanding these concepts enables prediction of chemical behavior across the periodic table

This concludes the lecture on periodic trends using Coulomb's Law as a foundational principle.