Lecture Summary: Periodic Trends

Overview

This lecture covers key periodic trends in the periodic table, including:

• Atomic and Ionic Radius
• Electronegativity
• Ionization Energy
• Electron Affinity
• Metallic Character

Atomic Radius

• Increase in Size:
  • Atomic size increases as you move to the left and down the periodic table.
  • Example: Hydrogen is larger than Helium despite having a smaller atomic mass.
• Key Factors:
  • Charge Attraction: More protons lead to greater attraction, reducing atomic size.
  • Distance Effect: Closer electrons to the nucleus experience stronger attraction.
• Trends:
  • Across a period: Size decreases due to increased proton charge.
  • Down a group: Size increases due to additional electron shells.

Ionic Radius

• Cations vs. Anions:
  • Cations (positively charged) are smaller than their parent atoms.
  • Anions (negatively charged) are larger than their parent atoms.
• Comparisons:
  • Ions with similar charges decrease in size across a period and increase down a group.
• Examples:
  • Sodium ion is larger than magnesium ion due to fewer protons.

Electronegativity

• Trends:
  • Increases towards the right and upwards the periodic table.
  • Highest in nonmetals (e.g., Fluorine is the most electronegative).
• Ranking Elements:
  • Elements within the same period or group can be ranked by their electronegativity.

Metallic Character

• Increase in Character:
  • Increases to the left and down the periodic table.
  • Metals are more likely to lose electrons, hence more metallic.
• Ranking by Character:
  • Elements can be ranked based on their position in the periodic table.

Ionization Energy

• Definition: Energy required to remove an electron from an atom.
• Trends:
  • Increases towards the right and upwards due to increased nuclear charge.
  • Decreases down a group due to increased distance of valence electrons from the nucleus.
• Exceptions: Occur due to electron configurations, e.g., between Be and B.

Electron Affinity

• Definition: Energy change when an electron is added to a gaseous atom.
• Trends:
  • Generally increases (becomes more exothermic) towards the right.
  • Less affinity in groups 2 and 8 due to stable configurations.
• Comparisons:
  • Group 7 elements have the highest electron affinity.

Practice Problems

• Examples provided for ranking elements by size, ionic radius, electronegativity, and other properties.
• Key trends and exceptions highlighted with specific examples from the periodic table.