What Is Electronegativity Difference?

Electrons are shared equally.

Examples:

• H₂
• Cl₂
• CH₄ (C–H is nearly nonpolar)

Nonpolar molecules tend to have:

• Low boiling points
• Low solubility in water
• Only London dispersion forces

2. Polar Covalent Bonds (ΔEN 0.5 – 1.7)

Electrons are shared unequally.

This creates:

• Partial positive charge (δ+)
• Partial negative charge (δ–)
• A permanent dipole

Examples:

• HCl (ΔEN = 0.9)
• H₂O (O–H ΔEN = 1.4)
• NH₃ (N–H ΔEN ≈ 0.9)

These substances have stronger intermolecular forces.

3. Ionic Bonds (ΔEN > 1.7)

Electrons are not shared.
One atom transfers its electron completely to another.

Example:

• NaCl: ΔEN ≈ 2.1
• MgO: ΔEN ≈ 2.7

Ionic compounds form lattice structures and have:

• High melting points
• High boiling points
• Good conductivity when molten or dissolved

IB Chemistry acknowledges that ionic character is continuous, but these ranges are good approximations.

Relationship Between Electronegativity Difference and Polarity

Greater ΔEN → More polar bond

Polarity arises because electrons shift toward the more electronegative atom.

Examples:

• C–O is more polar than C–H
• O–H is strongly polar
• N–H is moderately polar

These differences influence solubility and boiling point.

Molecular Polarity vs Bond Polarity

Even if bonds are polar, a molecule may be nonpolar if the dipoles cancel due to symmetry.

Examples of polar bonds but nonpolar molecules:

• CO₂ (linear)
• CCl₄ (tetrahedral)

Examples of polar molecules:

• H₂O (bent)
• NH₃ (trigonal pyramidal)

Molecular shape determines whether bond dipoles add up or cancel.

Impact of Electronegativity Difference on Physical Properties

1. Higher ΔEN = higher boiling point

Stronger dipole–dipole forces require more energy to separate molecules.

2. Higher ΔEN = higher solubility in water

Water dissolves polar and ionic substances due to strong polarity.

3. Higher ΔEN = more reactive

Ionic bonds break differently than covalent ones.

Common IB Misunderstandings

“If a molecule has polar bonds, it must be polar.”

Not necessarily—shape matters.

“Ionic bonds always have ΔEN above 1.7.”

Useful guideline, but real bonds exist on a spectrum.

“Electronegativity difference determines molecule shape.”

ΔEN affects bond polarity, not geometry.

“C–H is strongly polar.”

Incorrect—C–H is almost nonpolar.

FAQs

Why do electronegativity values increase across a period?

Because nuclear charge increases while shielding remains constant.

Why do ionic bonds form?

Large ΔEN values cause electrons to transfer rather than share.

Is ΔEN always enough to classify bonds?

It’s a good predictor, but real bonds often have mixed character.

Conclusion

Electronegativity difference measures how unevenly electrons are shared in a bond. It determines bond polarity, helps predict molecular polarity, and influences both physical and chemical properties. Understanding ΔEN is essential for mastering IB Chemistry bonding, molecular structure, and intermolecular forces.

Learn why the mole allows chemists to connect atomic-scale particles to measurable quantities used in real experiments.