Lecture on Periodic Table Trends

Introduction

• Focus on trends in the periodic table.
• Key trends to be discussed:
  • Atomic radius
  • Ionic radius
  • Metallic character
  • Electronegativity (part of electropositivity)
  • Ionization energy

Atomic Radius and Ionic Radius

Atomic Radius

• Trend Down a Group:
  • Atomic radius increases as you move down a group.
  • Increase in the number of protons (nuclear charge, Z) and electron shells.
  • Increased shielding effect due to more inner electron shells.
  • Effective nuclear charge decreases, leading to less attraction to valence electrons.
• Trend Across a Period:
  • Atomic radius decreases from left to right across a period.
  • Number of electron shells remains constant.
  • Increase in nuclear charge, Z, while shielding effect remains constant.
  • Valence electrons experience increased inward attraction, pulling them closer to the nucleus.

Ionic Radius

• Metals:
  • Metals lose valence electrons when forming positive ions.
  • Example: Sodium atom (Na) becomes smaller as it loses an electron to form Na+.
  • Positive ions are smaller than their neutral atoms.
• Non-Metals:
  • Non-metals gain electrons when forming negative ions.
  • Example: Phosphorus (P) gains electrons to become P³⁻, increasing in size.
  • Negative ions are larger than their neutral atoms.
  • Increased electron repulsion leads to a larger ionic radius.

Metallic Character and Electronegativity

Metallic Character and Electropositivity

• Trend Down a Group:
  • Valence electrons are held more weakly.
  • Easier to lose electrons, increasing electropositivity and metallic character.
• Trend Across a Period:
  • Harder to lose valence electrons across a period due to increased effective nuclear charge.
  • Metallic character decreases.

Electronegativity

• Trend Down a Group:
  • Decrease in electronegativity as electropositivity increases (easier to lose electrons).
• Trend Across a Period:
  • Increase in electronegativity as it becomes harder to lose electrons, making it easier to gain electrons.

Conclusion

• Next video will cover ionization energy in detail.