By Riti Gupta
Updated Aug 30, 2022
Emilija Randjelovic/iStock/GettyImages
When two atoms bond, the nature of that bond depends on how strongly each atom attracts shared electrons. This attraction is measured by electronegativity. By comparing electronegativity values, chemists can determine whether a bond is non‑polar covalent, polar covalent, or ionic.
Electronegativity is an atom’s ability to pull electron density toward itself in a chemical bond. While the concept is absolute, the values are always expressed relative to another element—there is no universal scale.
Atoms strive for a full valence shell, typically eight electrons. Elements that can more readily attract additional electrons are considered highly electronegative. Across the periodic table, electronegativity increases from left to right and from bottom to top, with the exception of transition metals.
The top‑right corner hosts the most electronegative elements: fluorine (3.98), oxygen (3.44), and chlorine (3.16). In contrast, alkali and alkaline earth metals on the lower left are the least electronegative.
When two atoms have a large difference in electronegativity, one atom typically pulls an electron from the other, forming an ionic bond. Example: sodium (0.93) vs. chlorine (3.16) gives a difference of 2.23, resulting in the ionic salt NaCl.
If the electronegativity difference is modest, the atoms share electrons. When the sharing is uneven—because one atom is more electronegative—the bond is polar covalent. If the electronegativities are identical, the bond is non‑polar covalent.
| Bond Type | Electronegativity Difference |
|---|---|
| Pure covalent | < 0.4 |
| Polar covalent | 0.4 – 1.8 |
| Ionic | > 1.8 |
Use the table to predict the bonding character of any compound.
Potassium fluoride (KF)
Potassium: 0.82, Fluorine: 4.00 → Δ = 3.18 (>1.8) → ionic bond.
Hydrogen chloride (HCl)
Hydrogen: 2.20, Chlorine: 3.16 → Δ = 0.96 (0.4–1.8) → polar covalent bond, with chlorine pulling electron density toward itself.
Understanding these principles allows you to quickly assess the nature of any chemical bond based on electronegativity differences.
