Understanding the Periodic Table Trends

Sep 25, 2024

Lecture Notes: The Periodic Table

Introduction

  • The periodic table is a familiar concept, even to those not specialized in chemistry.
  • Arranged in a way to reveal patterns in nature.

History and Development

  • Developed in mid-1800s by Dmitri Mendeleev.
  • Mendeleev's table was successful due to:
    • Correlation of data.
    • Predictive ability.
  • Elements arranged in:
    • Rows (Periods)
    • Columns (Groups)
  • Elements with similar behaviors are grouped together.
  • Predicted the existence and properties of undiscovered elements.

Arrangement Explanation

  • Elements in the same group have the same number of valence electrons.
  • Example:
    • Group 1: One valence electron.
    • Group 2: Two valence electrons.

Periodic Trends

1. Atomic Radius

  • Size of the atom.
  • Trend:
    • Increases moving downward due to added shells.
    • Decreases moving right due to increased proton pull within a shell.

2. Ionic Radius

  • Affected by electron gain/loss:
    • Adding an electron enlarges atom.
    • Removing an electron shrinks atom.
  • For ions with the same electron configuration, radius decreases with increasing atomic number.

3. Ionization Energy

  • Energy to remove an electron from the outermost shell.
  • Trend: Opposite to atomic radius.
    • Easier to ionize larger atoms (e.g., Francium).
    • Harder to ionize smaller atoms (e.g., Helium).
  • Successive ionization energies increase, with a notable jump when moving to a filled shell configuration.
  • Exceptions due to orbital symmetry, e.g.,:
    • Oxygen vs. Nitrogen: Oxygen has lower ionization energy due to orbital stability gain.

4. Electron Affinity

  • Energy change when an atom gains an electron.
  • Trend: Increases moving right (excluding noble gases).
    • Highest in Fluorine due to achieving a full shell.

5. Electronegativity

  • Ability of an atom to attract electrons.
  • Trend: Increases moving right and upward (excluding noble gases).
    • Important for understanding chemical bonds.

Conclusion

  • Key trends to remember:
    • Atomic Radius (downward increase).
    • Ionization Energy, Electron Affinity, Electronegativity (rightward increase).
  • Future learning will delve into chemical bonds.
  • Note: Lecture ends with a prompt to subscribe for further tutorials and a reminder to email for queries.