Polarity of Molecules

1. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
6.7 Electronegativity and Bond Polarity
The electronegativity
values of representative
elements in Group 1A
(1) to Group 7A (17).
Learning Goal Use
electronegativity to
determine the polarity
of a bond.

2. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Electronegativity
The electronegativity of an atom is its ability to
attract the shared electrons in a bond. It
• increases from left to right going across a period
on the periodic table.
• increases from the bottom to the top of the
periodic table.
• is high for the nonmetals, with fluorine as the
highest.
• is low for the metals.
Core Chemistry Skill Using Electronegativity

3. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Electronegativity and the Periodic Table

4. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Polarity of Bonds
The difference in
electronegativity of
bonding atoms can be
used to predict the
polarity of the bond.
In the H2 molecule,
electrons are shared
equally and the bond is
nonpolar. In the HCl
molecule, electrons are
shared unequally, and
the bond is polar.

5. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Nonpolar Covalent Bonds
A nonpolar covalent bond occurs between nonmetals. It
• is an equal or almost equal sharing of electrons by the two
bonding atoms.
• has a very small electronegativity difference between atoms.
Examples
Electronegativity
Atoms Difference Type of Bond
N-N 3.0 − 3.0 = 0.0 Nonpolar covalent
Cl-Br 3.0 − 2.8 = 0.2 Nonpolar covalent
H-Si 2.1 − 1.8 = 0.3 Nonpolar covalent

6. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Polar Covalent Bonds
A polar covalent bond occurs between nonmetal atoms. It
• is an unequal sharing of electrons.
• has a moderate electronegativity difference.
Examples
Electronegativity
Atoms Difference Type of Bond
O-Cl 3.5 − 3.0 = 0.5 Polar covalent
Cl-C 3.0 − 2.5 = 0.5 Polar covalent
O-S 3.5 − 2.5 = 1.0 Polar covalent

7. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Dipoles and Bond Polarity
A polar covalent bond becomes more polar as the difference in
electronegativity increases. The separation of charges in a polar
bond is called a dipole.
The positive and negative ends of the dipole are located by using
• the lowercase Greek letter delta with a positive or negative
charge.
• an arrow that points from the positive to the negative end of
the dipole.

8. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Ionic Bonds
An ionic bond
• occurs between metal and nonmetal ions.
• is a result of electron transfer.
• has a large electronegativity difference (1.8 or more).
Examples
Electronegativity
Atoms Difference Type of Bond
Cl-K 3.0 – 0.8 = 2.2 Ionic
N-Na 3.0 – 0.9 = 2.1 Ionic
S-Cs 2.5 – 0.7 = 1.8 Ionic

9. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Variations in Bonding
The difference in electronegativity values for two
atoms can be used to predict the type of chemical
bond. If the electronegativity difference is
• between 0 and 0.4, the bond is nonpolar
covalent.
• between 0.5 and 1.8, the bond is polar covalent.
• greater than 1.8, the bond is ionic and the
electrons are considered transferred.

10. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Electronegativity and Bond Types

11. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Predicting Bond Type Using
Electronegativity

12. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Study Check
Use the electronegativity difference to identify
the type of bond (nonpolar covalent [NP], polar
covalent [P], or ionic [I]) between the following:
A. K—N
B. N—O
C.Cl—Cl
D.H—Cl

13. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Solution
Use the electronegativity difference to identify
the type of bond (nonpolar covalent [NP], polar
covalent [P], or ionic [I]) between the following:
Difference Type of bond
A. K—N 2.2 ionic (I)
B. N—O 0.5 polar covalent (P)
C.Cl—Cl 0.0 nonpolar covalent (NP)
D.H—Cl 0.9 polar covalent (P)