Electronegativity & Bond Polarity in IB Chemistry: The Complete FAQ

You need to link electronegativity values to bond type — ionic, polar covalent, nonpolar covalent — explain the periodic trend, and combine bond polarity with molecular shape to predict overall molecular polarity. This content sits under Structure 2.2 of the current IB Chemistry guide, first examined in 2025.

Electronegativity is an atom's relative ability to attract the shared electron pair in a covalent bond towards itself. The IB uses the Pauling scale, printed in Section 8 of the data booklet, where fluorine (3.98) is the most electronegative element and caesium (0.79) sits near the bottom.

A polar bond exists whenever two bonded atoms have different electronegativities — that's purely a bond property. A polar molecule depends on the whole shape: if the individual bond dipoles don't cancel through symmetry, the molecule is polar overall. Get this distinction wrong and half your bonding answers unravel.

Large electronegativity differences favour electron transfer and ionic bonding; small or zero differences favour sharing — nonpolar covalent between identical atoms, polar covalent between different nonmetals. Metallic bonding occurs between atoms with low, similar electronegativities that delocalise their electrons rather than sharing or transferring them.

Electronegativity increases across a period, because more protons pull on electrons in a similar-sized shell, and decreases down a group, because increased shielding and atomic radius outweigh the extra nuclear charge. Fluorine is the most electronegative element on the Pauling scale; caesium and francium sit near the bottom.

No — you don't memorise numbers. The IB Chemistry data booklet (Section 8) gives Pauling electronegativity values for every element, so exam questions test whether you can read, compare and apply those values under time pressure, not recall them from memory.

The IB doesn't set one official numerical cutoff — bonding character is a continuum, not a hard line. Most teachers use rough guide bands (below ~0.4 nonpolar, 0.5–1.6 polar covalent, 1.7+ mostly ionic), but examiners want reasoned discussion of the trend, not a memorised threshold quoted as fact.

Paper 1 favours short multiple-choice items ranking electronegativity or spotting bond polarity from a structural diagram. Paper 2 asks you to justify bond type or molecular polarity using data booklet values, usually combined with VSEPR shape and intermolecular force reasoning in longer structured responses worth 3-6 marks.

Forgetting that molecular polarity depends on shape, not just bond polarity. Students correctly identify polar C–Cl or C–F bonds, then wrongly call CCl4 or CF4 'polar' — but both are tetrahedral and perfectly symmetric, so the bond dipoles cancel and the molecule is nonpolar overall.

Follow three steps: identify each bond's polarity from electronegativity differences, determine the molecular shape using VSEPR, then check whether the bond dipoles cancel by symmetry. If they cancel, the molecule is nonpolar overall; if there's a net dipole left over, the molecule is polar.

Practise past-paper questions that combine electronegativity with VSEPR shapes and intermolecular forces — that's where marks are actually lost, not on the definitions. Build a quick-reference table of common molecules and their shape/polarity, then test yourself without the data booklet before checking your answers against it.

The core concept is identical for SL and HL, but HL students apply it more rigorously — linking bond polarity to dipole-dipole forces, hydrogen bonding strength, and even reaction mechanisms in the Reactivity topics. SL questions usually stop at identifying polarity and its effect on physical properties.

Nearly always it's the shape step being skipped — your child identifies a polar bond correctly but forgets to check the molecule's overall symmetry using VSEPR before deciding if the whole molecule is polar. That one missing step accounts for a large share of the marks lost on this topic in Paper 2.

Look for resources pairing concise notes with plenty of past-paper-style practice, since this topic is examined through application rather than recall. On revisionprep.com, the Chemistry Revision Notes and Topical Worksheets cover Structure 2.2 with worked bond-polarity questions, and Mock Papers help test exam timing under real conditions.