Polar and Non-Polar Covalent Bonds
If an electron pair is shared equally between two bonding atoms, the bond is
called nonpolar covalent.
Examples: diatomic elements such as H2, N2, Cl2 where the nuclei attract electrons
with equal force.
When the sharing of bonding valence electrons is not equal and one nucleus
pulls the bonding electrons with greater force than the other atom’s nucleus, the
bond is called a polar covalent bond.
Example: Hδ+ — Clδ-
where δ+ means partially positive charge and
δ- means partially negative charge.
In a hydrogen chloride molecule, the bonding electrons spend a
greater amount of time in the space close to the chlorine nucleus because
Chlorine has a much higher electronegativity than Hydrogen.
Polar Molecules
Polar molecules are molecules that have a positively charged end and a
negatively charged end. Both polar bonds and 3D molecular shape
affects polarity.
Polar or Non-Polar?
Example #1. Ammonia
δN
H
H
H
δ+
 Nitrogen has higher electronegativity than Hydrogen
 Nitrogen pulls the bonding electron pairs close to its nucleus
 Also, consider the contribution of the non-bonding electrons of
Nitrogen
 NH3 is a polar molecule: one end is negatively charged (N) and the
other end is positively charged (H)
Example #2. Methane
The central carbon atom is
surrounded by identical
Hydrogen atoms that are
equivalent in
electronegativity value;
they pull on electrons with
equal force. The “net
pull” is zero.
CH4 (methane) is a nonpolar molecule.
H
C
H
H
H
Example 3. Carbon dioxide
O=C=O
The central Carbon atom is aligned between two identical Oxygen
atoms. Both Oxygen atoms pull on the bonding electrons with equal
force. As a result, this molecule is non-polar.
{Analogy: Tug-of-war, the carbon atom does not move when pulled on
either side by Oxygen atoms of equal strengths.)
Consider:
Replace one Hydrogen atom of methane with a chlorine atom; chemical
formula, CH3Cl.
Is this molecule polar or non-polar? Explain.