What is Electronegativity?
Electronegativity is the relative ability of an atom to attract electrons in a chemical bond. Unlike ionization energy (property of isolated atoms) and electron affinity (property of isolated atoms), electronegativity describes an atom's competitive advantage in a bonding situation. The Pauling scale (0–4) quantifies it: higher values mean stronger electron attraction.
Electronegativity is how strongly an atom attracts electrons in a bond, measured on the Pauling scale (0–4). Fluorine (4.0) is the most electronegative; cesium (0.7) is least. Electronegativity differences predict bond type: >2.0 = ionic, 0.5–2.0 = polar covalent, <0.5 = nonpolar covalent.
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Step-by-step worked examples
Determine bond type in HF. Use Pauling electronegativities: H = 2.1, F = 4.0.
ΔEN = |4.0 − 2.1| = 1.9 Since 1.5 < ΔEN < 2.0, HF is a POLAR COVALENT bond. F attracts the shared electron pair strongly → bond is polarized (H is δ+, F is δ−).
Classify the C-C bond in ethane (CH₃-CH₃). C = 2.6.
ΔEN = |2.6 − 2.6| = 0 Since ΔEN ≈ 0 (< 0.5), C-C is a NONPOLAR COVALENT bond. Electron density is equally shared — no polarity.
Classify the Na-Cl bond. Na = 0.9, Cl = 3.0.
ΔEN = |3.0 − 0.9| = 2.1 Since ΔEN > 2.0, Na-Cl is an IONIC bond. Cl strongly attracts electron → electron transfers from Na to Cl → Na⁺ and Cl⁻ ions.
Flashcards
Quick quiz
Q1.Electronegativity measures…
Q2.Bond in H-Cl: H = 2.1, Cl = 3.0. ΔEN = ?
Q3.Which bond is most polar?
Q4.Electronegativity trend down a group…
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Common mistakes
Electronegativity is a property of isolated atoms like ionization energy. — Correct: EN is a RELATIVE measure of electron attraction IN A BOND between two atoms. IE applies to isolated atoms.
Halogens and noble gases have the same electronegativity. — Correct: Halogens (Cl, F) have high EN — they attract electrons in bonds. Noble gases have high EN but are rarely bonded.
A bond with ΔEN = 0.8 is ionic. — Correct: 0.8 is in the polar covalent range (0.5–2.0). Ionic bonds require ΔEN > 2.0.
Electronegativity increases left-to-right like ionization energy. — Correct: EN does increase left-to-right, BUT also trends differently due to bonding context (not just isolated atom properties).
FAQ
Why did Linus Pauling create the EN scale?
Pauling needed a quantitative way to describe bond polarity and predict when atoms form ionic vs covalent bonds. He empirically measured EN based on bond energies.
Can electronegativity exceed 4.0?
On Pauling scale, F = 4.0 is the max (officially 3.98). Some modern scales extend beyond 4 for superheavy elements.
Does electronegativity predict chemical reactivity?
Partly — high EN elements (F, Cl) readily gain electrons (strong oxidizers); low EN metals (Na, K) readily lose electrons (strong reducers). But full reactivity requires context (partner element, reaction type).
How does EN relate to chemical bonding types?
EN difference predicts bond polarity and electron distribution. Same-EN elements (C-C) form nonpolar covalent; different EN (H-F) form polar covalent; very different EN (Na-Cl) form ionic.