What is Bond Polarity and Electronegativity?
Electronegativity is an atom's tendency to attract electrons in a bond. When two atoms with different electronegativities bond, electron density shifts toward the more electronegative atom, creating a polar bond. The greater the electronegativity difference, the more polar the bond.
Bond polarity measures how unevenly electrons are shared in a bond. Electronegativity (Pauling scale, 0–4) quantifies an atom's electron-attracting power. Larger Δ-electronegativity → more polar bond.
Step-by-step worked examples
Compare the polarity of H–H and H–Cl bonds.
H–H: both atoms have electronegativity 2.1 → Δ = 0 → nonpolar bond H–Cl: H = 2.1, Cl = 3.16 → Δ = 1.06 → polar bond (Cl pulls electrons, forms δ− charge) Conclusion: H–H is nonpolar; H–Cl is polar
Predict the bond polarity in C–O and C–N bonds.
C–O: C = 2.55, O = 3.44 → Δ = 0.89 → moderately polar (O is more electronegative) C–N: C = 2.55, N = 3.04 → Δ = 0.49 → weakly polar (N is more electronegative) Conclusion: C–O is more polar than C–N due to larger Δ-electronegativity
Explain why HF is the most polar hydrogen halide.
H = 2.1, F = 3.98 → Δ = 1.88 (largest among H–X) Comparison: H–F (1.88) > H–Cl (1.06) > H–Br (0.76) > H–I (0.46) F's high electronegativity creates the largest electron shift → most polar bond
Flashcards
Quick quiz
Q1.Electronegativity measures an atom's ability to…
Q2.The Pauling electronegativity scale ranges from…
Q3.Which bond is most polar?
Q4.A bond with Δ-electronegativity = 0 is…
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Common mistakes
Confusing electronegativity with electron affinity or ionisation energy. — Correct: Electronegativity = electron-attracting power in a bond; affinity/ionisation = standalone atomic property.
Assuming all H–X bonds are equally polar. — Correct: Polarity depends on the electronegativity difference: H–F >> H–Cl > H–Br > H–I.
Thinking ionic bonds have zero polarity. — Correct: Ionic bonds have extreme polarity; electrons essentially transferred, not just shifted.
Ignoring that polarity affects molecule properties. — Correct: Polar bonds → polar molecules (if geometry allows) → higher boiling point, solubility in water, dipole moment.
FAQ
How is the Pauling electronegativity scale determined?
Pauling calculated values from bond dissociation energies, setting F = 3.98 as the reference (highest). Other elements are calibrated relative to F.
Why does electronegativity increase left-to-right across a period?
As nuclear charge increases (more protons) while electrons are in the same shell, the nucleus pulls electrons closer → higher electronegativity.
Can a molecule be polar if all bonds are nonpolar?
Yes — if the dipole moments of nonpolar bonds cancel (e.g., CO₂ has two polar C=O bonds, but geometry cancels them → nonpolar molecule).
What does δ+ and δ− mean?
δ+ = partial positive charge on the less electronegative atom; δ− = partial negative charge on the more electronegative atom in a polar bond.