Electronegativity & Polarity

Electronegativity measures how strongly an atom pulls a shared electron pair, and it grows toward the top right of the periodic table. Equal electronegativities give a nonpolar covalent bond; a difference gives a polar one with partial charges. Even polar bonds can cancel in a symmetric molecule, so molecular shape decides overall polarity. Here you change ΔEN to watch partial charges form and reason about shape and polarity together.

Who Pulls the Electrons Harder

Electronegativity difference ΔEN1.5

👀 See It

①Electronegativity is how strongly an atom pulls the shared electron pair

②Equal electronegativity keeps the pair centered — nonpolar

③A large difference shifts the pair to one side, making δ− (the puller) and δ+ (the other)

Electronegativity and Bond Polarity

Electronegativity trend

increases toward the upper right of the periodic table (F is the max)

Within a period it rises to the right; within a group, upward

Bond polarity

ΔEN = 0 → nonpolar covalent, ΔEN > 0 → polar covalent

The larger the electronegativity difference, the more polar the bond (partial charges)

Molecular Polarity — Shape Matters

🧭 Bond Polarity + Molecular Shape

①Even with polar bonds, a symmetric molecule cancels them out — nonpolar

②CO₂ is linear and symmetric → nonpolar molecule

③H₂O is bent (asymmetric) → polar molecule

Reason It Out

Example 1

Explain the partial-charge distribution and bond polarity in HCl.

Electronegativity is Cl > H.

The shared electron pair shifts toward Cl.

Cl: δ−, H: δ+ ⇒ polar covalent bond

▸ Polar covalent: δ− on Cl, δ+ on H

The more electronegative atom always becomes δ−.

Example 2

CO₂ and H₂O both have polar bonds, so why is their molecular polarity different?

Both molecules have polar bonds themselves.

Whether they cancel depends on molecular shape.

CO₂ (linear·symmetric) → cancels → nonpolar / H₂O (bent) → polar

▸ CO₂ nonpolar, H₂O polar (shape difference)

Even with polar bonds, a symmetric shape makes a nonpolar molecule.

Wrap-up

Key result

bond polarity = ΔEN, molecular polarity = bond polarity + shape (symmetry)

Bond polarity from ΔEN; add the shape to judge molecular polarity

2021 CSAT Science (Chemistry Ⅰ) type, adapted

Which of the following is a nonpolar molecule? (HF, H₂O, NH₃, CO₂, HCl)

①HF

②H₂O

③NH₃

④CO₂

⑤HCl

▸ ④ CO₂

Check each shape — CO₂ is linear and symmetric.

Symmetry cancels the bond polarities.

CO₂: linear symmetric ⇒ nonpolar molecule

🎯 Exam Points

①electronegativity: larger toward upper-right (F max)

②ΔEN=0 nonpolar bond, ΔEN>0 polar bond

③the more electronegative atom is δ−

④molecular polarity = bond polarity + shape (symmetry = cancellation)

⑤CO₂ nonpolar vs H₂O polar is the classic comparison

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Molecular Structure

Chemical Equations and Stoichiometry

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