Lecture Notes on Electronegativity

Definition and Importance

• Electronegativity: Ability of an atom to attract electrons to itself.
  • Example: Fluorine is highly electronegative, desires to fill its outer energy level (octet rule).
  • Halogens (e.g., fluorine, chlorine, bromine) are electronegative, want to gain an electron.
  • Metals (e.g., sodium) are electropositive, prefer to give away electrons to form cations.

General Trends

• Nonmetals tend to be electronegative (attract electrons).
• Metals tend to be electropositive (donate electrons).

Periodic Table Trends

• Across a Period: Electronegativity increases as you move right.
  • Examples:
    • Boron (2.0), Carbon (2.5), Nitrogen (3.0), Oxygen (3.5), Fluorine (4.0).
• Down a Group: Electronegativity decreases as you move down.

Notable Values

• Hydrogen: 2.1
• Fluorine: 4.0 (most electronegative)
• Noble Gases: No electronegativity values (stable and do not attract electrons).

Practice Problems

Problem Set

Part A: Chromium vs. Arsenic

• Arsenic (2.0) > Chromium (1.6)
  • Arsenic is more electronegative than chromium.

Part B: Calcium vs. Zinc

• Zinc (1.6) > Calcium (1.0)
  • Zinc is more electronegative than calcium.

Part C: Selenium vs. Tellurium

• Selenium (2.4) > Tellurium (2.1)
  • Selenium is more electronegative because it's higher in the group.

Part D: Chlorine Cation vs. Chlorine Anion

• Chlorine Cation is more electronegative than the chloride ion.
  • Positively charged ions typically have higher electronegativity than negatively charged ones.

Part E: Nickel 2+ vs. Nickel 3+

• Nickel 3+ is more electronegative than nickel 2+.
  • Higher positive charge increases electronegativity.

Ranking Elements by Electronegativity

• Order (Increasing): Rubidium (0.8) < Manganese (1.5) < Copper (1.9) < Phosphorus (2.1) < Oxygen (3.5)
  • Oxygen is the most electronegative, rubidium is the least.

Summary

• Electronegativity is essential for understanding how atoms interact in chemical reactions and bonding.
• The trend generally increases towards fluorine across the periodic table.
• Positive ions tend to exhibit greater electronegativity compared to their neutral or negatively charged counterparts.