Aim: What are polar
bonds and polar
molecules?
Polar and Nonpolar Bonds
• There are two types of covalent bonds
• Nonpolar Covalent Bonds (equal share of electrons)
• Polar Covalent Bonds (unequal share of electrons)
Polar Covalent Bond
• A Polar Covalent Bond is unequal sharing of
electrons between two atoms (H-Cl)
• In a polar covalent bond, one atom typically has a
negative charge, and the other atom has a positive charge
Nonpolar Covalent Bond
• A Nonpolar Covalent Bond is an equal sharing of
electrons between two atoms (Cl-Cl, N-N, O-O)
Classification of Bonds
You can determine the type of bond between two atoms by calculating
the difference in electronegativity values between the elements
The bigger the electronegativity difference the more polar the bond.
Type of Bond
Nonpolar Covalent
Electronegativity
Difference
0  0.4
Polar Covalent
0.5  1.9
Ionic
2.0  4.0
Practice
What type of bond is HCl? (H = 2.1, Cl = 3.1)
Difference = 3.1 – 2.1 = 1.0
Therefore it is polar covalent bond.
Your Turn To Practice
 N(3.0) and H(2.1)
 Al(1.5) and Cl(3.0)
 H(2.1) and H(2.1)
 Mg(1.2) and O(3.5)
 Ca(1.0) and Cl(3.0)
 H(2.1) and F(4.0)
How to show a bond is polar
• Isn’t a whole charge just a partial charge
• d+ means a partially positive (less electronegative)
• d- means a partially negative (more electronegative)
d+
H
d-
Cl
• The Cl pulls harder on the electrons
• The electrons spend more time near the Cl
Polar Molecules
• Molecules with a positive and a negative end
• Requires two things to be true
 The molecule must contain polar bonds
This can be determined from differences in
electronegativity.
Asymmetric molecule.
Symmetrical Molecules
• Because of symmetry, molecules that have polar bonds
are overall a nonpolar molecules (+ and – charges
cancel out or balance out)
• Examples:
• CO2
BF3
• CCl4
Asymmetrical Molecules
• If a molecule has polar bonds (and there is no
symmetry to cancel out + and – charges), the molecule
is polar.
• Examples:
• H2O
HCl
• NH3
Dipole
When there is unequal sharing of electrons a dipole
exists
Dipole is a molecule that has two poles or regions
with opposite charges
A dipole is represented by a
dipole arrow pointing towards
the more negative end
Practice Drawing Dipoles
P- Br
P = 2.1
Br = 2.8
P –Br
d+
Practice
 H(2.1) – S(2.5)
 F(4.0) - C(2.5)
 C(2.5) - Si(1.8)
 N(3.0) – O(3.5)
d-
Is it Polar?
• HF
• H2O
• NH3
• CF4
• CO2
Summary
• In a polar bond, one atom is more electronegative than the
other.
• In a nonpolar bond, both atoms have similar
electronegativities.
• An asymmetric molecule with polar bonds is a polar molecule.
• An asymmetric molecule with nonpolar bonds is a nonpolar
molecule.
• A symmetric molecule, regardless of the polarity of the bonds,
is always a nonpolar molecule.