Electronegativity and bonding — common mistakes

A classic exam question involves comparing CO₂ and SO₂. Both have polar bonds. However, CO₂ is linear, so its two bond dipoles are equal and opposite, cancelling to zero, making the molecule non-polar. SO₂ is bent (due to a lone pair on the sulfur atom), so its bond dipoles do not cancel, resulting in a net dipole moment and a polar molecule. Always consider the VSEPR shape!

Usually, you are expected to know the general trends (increasing across a period, decreasing down a group). If a question requires a specific calculation of ΔEN, the values will almost always be provided in a data table.

No, the value of ΔEN ≈ 1.7 is just a useful guideline. Bonding is a continuum. Some compounds with a ΔEN below 1.7 show ionic characteristics, while some above it have covalent character. The key concept is that ionic character increases as ΔEN increases.

Electronegativity is defined for an atom attracting electrons within a covalent bond. Since noble gases have a full valence shell, they are very stable and do not readily form covalent bonds. Therefore, the concept of electronegativity is not typically applied to them.