IB Definition
"Bond polarity results from the difference in electronegativities of the bonded atoms." Electronegativity is the ability of an atom to attract a shared pair of electrons toward itself in a covalent bond.
Key Electronegativity Values
| Element | Pauling EN | Element | Pauling EN |
|---|---|---|---|
| F | 4.0 | C | 2.6 |
| O | 3.4 | H | 2.2 |
| N / Cl | 3.0 | Na | 0.9 |
The Bonding Continuum
Pure covalent
e.g. H₂, Cl₂
Polar covalent
e.g. H-Cl
Ionic
e.g. NaCl
In a polar bond, the more electronegative atom carries a partial negative charge (δ⁻) and the less electronegative atom carries a partial positive charge (δ⁺). This creates a bond dipole.
Examiner Trap
The 1.7 threshold is a guideline, not a rule. Some compounds with ΔEN > 1.7 are still covalent (e.g. HF, ΔEN = 1.8). The IB treats bonding as a spectrum, not a binary classification.
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