Electronegativity and Bond Polarity Explained

For example:

• H and Cl: ΔEN ≈ 0.9 → polar covalent
• C and H: ΔEN ≈ 0.4 → mostly non-polar
• Na and Cl: ΔEN ≈ 2.1 → ionic

These values aren’t strict boundaries but helpful guidelines that appear frequently in IB exam questions.

Why Polarity Matters

Polarity affects almost every major chemistry topic:

• Intermolecular forces: Polar molecules attract via dipole–dipole forces.
• Solubility: “Like dissolves like” — polar dissolves polar.
• Boiling points: Polar compounds show stronger forces and higher boiling points.
• Reactivity: Bond polarity influences reaction mechanisms, such as nucleophilic attack.
• Molecular shape and dipole moment: VSEPR and polarity work hand-in-hand.

This is why examiners test electronegativity so frequently—it links directly to molecular behaviour.

Example: Which Bond Is More Polar?

Consider the following bonds:

1. C–O
2. C–Cl
3. C–H

Electronegativity values (Pauling scale):

• C = 2.5
• O = 3.5
• Cl = 3.0
• H = 2.1

Calculate ΔEN:

1. C–O: 3.5 – 2.5 = 1.0
2. C–Cl: 3.0 – 2.5 = 0.5
3. C–H: 2.5 – 2.1 = 0.4

Ranking (most → least polar): C–O > C–Cl > C–H

This type of ranking question appears constantly in IB Paper 1 and Paper 2.

Common IB Mistakes to Avoid

• Forgetting molecular geometry: A molecule can contain polar bonds but still be non-polar if the shape is symmetrical (e.g., CO₂).
• Memorizing instead of reasoning: Use ΔEN to justify polarity—it earns marks on structured questions.
• Confusing bond polarity with molecular polarity: They are related but not identical.
• Assuming ionic/covalent boundaries are rigid: The ΔEN values give trends, not absolute rules.

FAQs

Why do noble gases have no electronegativity values?

Most noble gases do not form stable compounds, so they do not regularly share electrons in bonds. If bonding does occur, it is rare, and therefore assigning electronegativity values is not meaningful for most cases.

Can a molecule with polar bonds be non-polar overall?

Yes. If bond dipoles cancel because of symmetrical geometry (like in CO₂ or CCl₄), the molecule becomes non-polar. IB Chemistry often tests this by combining electronegativity knowledge with VSEPR shapes.

Do metals have low electronegativity?

Generally, yes. Metals have low electronegativity because they lose electrons easily, forming cations. This is why metal–non-metal pairs typically form ionic bonds with large electronegativity differences.

Conclusion

Electronegativity governs how electrons are shared in a bond, and understanding this concept allows you to determine whether a bond is polar or non-polar. This skill is foundational for mastering intermolecular forces, molecular geometry, solubility, and reaction mechanisms. By focusing on electronegativity differences and practicing comparisons, you’ll strengthen your understanding across multiple IB Chemistry topics.

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