Electronegativity and Bond Type
Simple Explanation
Electronegativity measures how strongly an atom attracts shared electrons in a bond. The difference in electronegativity between two bonded atoms determines what kind of bond forms: a small difference gives a covalent bond with electrons shared fairly evenly; a large difference means one atom pulls the electrons almost completely away, forming an ionic bond.
Why Do We Need It?
This single number lets you predict, before even looking anything up, whether two elements will form an ionic compound, a polar covalent bond, or a nonpolar covalent bond.
Formula
Electronegativity Difference
ΔEN = |EN₁ − EN₂|
How unequally two bonded atoms share their electrons — the bigger the difference, the more one-sided the bond.
- ΔEN
- — electronegativity difference between the two bonded atoms (no units — the Pauling scale is a relative scale)
- EN₁, EN₂
- — the Pauling electronegativity values of each atom in the bond
When to use it: Whenever you need to predict what type of bond forms between two atoms: roughly ΔEN < 0.4 is nonpolar covalent, 0.4–1.7 is polar covalent, and ΔEN > 1.7 is ionic.
Worked Example
Predict the bond type between sodium and chlorine
Sodium has an electronegativity of 0.93; chlorine has an electronegativity of 3.16. Find ΔEN and predict the bond type.
Why Does This Work?
When one atom is much more electronegative than the other, it doesn't just share the bonding electrons unevenly — it pulls them almost entirely to itself, effectively transferring the electron and creating two ions held together by electrostatic attraction, rather than a shared electron cloud.
Real-Life Example
Water is polar, oxygen gas is not
Water (H–O–H) is a polar molecule, but oxygen gas (O=O) is completely nonpolar.
In O=O, both atoms are identical, so ΔEN = 0 and the electrons are shared perfectly evenly. In O–H, oxygen (EN 3.44) is noticeably more electronegative than hydrogen (EN 2.20), giving ΔEN ≈ 1.24 — enough to make each O–H bond polar, which is why water molecules interact so strongly with each other.
Practice
Carbon has an electronegativity of 2.55; hydrogen has 2.20. Find ΔEN for a C–H bond.
MediumCommon mistake
Treating the 0.4/1.7 cutoffs as sharp, exact boundaries — real bonding exists on a continuous spectrum from purely covalent to purely ionic, and these numbers are just useful guidelines, not hard physical laws.
Quick Review
- ΔEN = |EN₁ − EN₂| predicts bond type.
- ΔEN < 0.4: nonpolar covalent. 0.4–1.7: polar covalent. ΔEN > 1.7: ionic.
- Bigger electronegativity differences mean more one-sided electron sharing.