Trends in the Periodic Table Explained

Nov 22, 2024

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.