Electronegativity and Bond Polarity
Quick Notes
- Electronegativity is an atom’s ability to attract the shared electrons in a covalent bond.
- A polar bond occurs when there is a difference in electronegativity between the bonded atoms.
- The greater the difference, the more polar the bond.
- We can use electronegativity values (from the IB data booklet) to:
- Determine if a bond is non-polar or polar
- Identify the direction of the bond dipole
- Bond dipoles can be shown using:
- δ⁺ / δ⁻ partial charges
- Vector arrows pointing toward the more electronegative atom
Full Notes:
What Is Electronegativity?
Electronegativity is a measure of how strongly an atom attracts shared electrons in a covalent bond.
- High electronegativity = strong pull on bonding electrons
- he Pauling scale is used to measure electronegativity and values are found in the IB Chemistry data booklet
Example: Fluorine (F) has the highest electronegativity (≈ 4.0). Cesium (Cs) has a very low electronegativity.
When Is a Bond Polar?
A bond is polar when there is a difference in electronegativity between the two bonded atoms.
- The electrons are unequally shared, resulting in partial charges:

The more electronegative atom becomes δ⁻ and the less electronegative atom becomes δ⁺
Example:Hydrogen Chloride (HCl):

- Chlorine (Cl) is more electronegative than Hydrogen (H)
- he bonding electrons are pulled closer to Cl, giving it δ⁻ while H becomes δ⁺
How to Deduce Bond Polarity
Follow these steps:
- Look up the electronegativity values in the data booklet.
- Subtract to find the difference (ΔEN).
- Interpret the result:
ΔEN (Electronegativity Difference) | Bond Type | Explanation |
---|---|---|
> 1.7 | Ionic | One atom takes the bonding electrons completely, forming ions. |
0.5 – 1.7 | Polar Covalent | Electrons shared unequally, producing δ⁺ and δ⁻ charges. |
0 – 0.4 | Non-polar Covalent | Electrons shared equally between atoms. |
If the difference is large (typically > 1.7), the bond is ionic.
One atom essentially takes the bonding electrons for itself. The atom with the higher electronegativity becomes a negatively charged ion and the atom with a lower electronegativity becomes a positively charged ion.
If the difference is moderate (between ~0.5 and 1.7), the bond is polar covalent.
The bonding electrons are shared unequally. The atom with the higher electronegativity has a partial negative charge (δ⁻) and the other atom a partial positive (δ⁺).
If the difference is very small or zero, the bond is non-polar covalent.
The bonding electrons are shared equally.

Always remember it is the difference in electronegativity between two bonding atoms that matters when determining whether a bond will be ionic, polar covalent, or non-polar covalent.
Examples:

- NaCl: large difference → ionic
- HCl: moderate difference → polar covalent
- Cl2: no difference → non-polar covalent
Representing Bond Polarity
We can show bond dipoles in two ways:

- Partial charges: δ⁺ and δ⁻
- Vector arrow → pointing toward the more electronegative atom
Summary
- Bond polarity depends on the difference in electronegativity between atoms.
- We can use electronegativity values to determine if a bond is polar, non-polar, or ionic.
- Show dipoles using δ⁺/δ⁻ notation or vector arrows.
- Bond polarity explains molecular polarity, intermolecular forces, and solubility.