1. Electronegativity and Polarity
Chem 332 – O’Dette

2. How do you determine the polarity of a molecule?
Based on polarity of bonds and shape of the molecule
Depends on the electronegativity of the elements in the molecule

3. What is electronegativity?
Ability of an element to attract electrons
Look up the values in a table
“Tug of War”

4. Electronegativity Difference
Polarity of Bonds
Type of Bond
Electronegativity Difference
Between Atoms
Nonpolar Covalent
0 – 0.4
Polar Covalent
0.5 – 1.8
Ionic
1.9 – 3.3

5. Polarity of Covalent Bonds
Nonpolar Covalent
What happens with the electrons in a nonpolar covalent bond?
Electrons are shared equally between the atoms
EX: H2
H – H
H : H
Electronegativity
H = H = 2.1
Difference = 0

6. Polarity of Covalent Bonds
Polar Covalent
What happens with the electrons in a polar covalent bond?
Electrons are shared unequally between the atoms
EX: HBr
H – Br:
H : Br
Electronegativity
H = Br = 2.8
Difference = 0.7 :
Br has a stronger pull on the electrons

7. Polarity of Ionic Bond Ionic
What happens with the electrons in a ionic bond?
Electrons are completely transferred
Ex: NaCl

9. : Polarity of Molecules NH3 vs. CO2 H – N – H : O = C = O : H
Is it possible to have a compound with polar bonds in it but for the compound itself to be nonpolar?
NH vs CO2
H – N – H : O = C = O : H :
Electronegativity
N = 3 H = 2.1
Difference = 0.9
Electronegativity
C = O = 3.5
Difference = 1
Polar Bond
Polar Bond
Polar Molecule
Nonpolar Molecule

10. Polarity of Molecules
Even if the bonds between atoms are polar, the overall molecule polarity is nonpolar if
There are no lone pairs on central atom
Elements surrounding central atom are the same

11. : Concept Check What is the polarity of the following molecule? COS
: S = C = O : :
Polar