1. Bonds & Polarity Review:
Electronegativity and Bond Polarity
Copyright © by Pearson Education, Inc.
Publishing as Benjamin Cummings

2. Electronegativity The electronegativity value
indicates the attraction of an atom for shared electrons.
increases from left to right going across a period on the periodic table.
is high for the nonmetals with fluorine as the highest.
is low for the metals.

3. Some Electronegativity Values for Group A Elements
Electronegativity decreases `
Electronegativity increases
High values `
Low values
Copyright © by Pearson Education, Inc.
Publishing as Benjamin Cummings

4. Nonpolar Covalent Bonds
A nonpolar covalent bond
occurs between nonmetals.
is an equal or almost equal sharing of electrons.
has almost no electronegativity difference (0.0 to 0.4).
Examples:
Electronegativity
Atoms Difference Type of Bond
N-N = Nonpolar covalent
Cl-Br = Nonpolar covalent
H-Si = Nonpolar covalent

5. Polar Covalent Bonds A polar covalent bond
occurs between nonmetal atoms.
is an unequal sharing of electrons.
has a moderate electronegativity difference (0.5 to 1.9).
Examples:
Electronegativity
Atoms Difference Type of Bond
O-Cl = 0.5 Polar covalent
Cl-C = 0.5 Polar covalent
O-S = 1.0 Polar covalent

6. Comparing Nonpolar and Polar Covalent Bonds
Copyright © by Pearson Education, Inc.
Publishing as Benjamin Cummings

7. Ionic Bonds An ionic bond occurs between metal and nonmetal ions.
is a result of electron transfer.
has a large electronegativity difference (1.9 or more).
Examples:
Electronegativity
Atoms Difference Type of Bond
Cl-K – 0.8 = Ionic
N-Na 3.0 – = Ionic
S-Cs 2.6 – 0.7 = Ionic

8. Electronegativity and Bond Types
TABLE 4.14

9. Predicting Bond Types
Table 4.15

10. Learning Check
Use the electronegativity difference to identify the type of bond between the following:
nonpolar covalent (NP), polar covalent (P), or
ionic (I).
A. K-N
B. N-O
C. Cl-Cl
D. H-Cl

11. Solution
Use the electronegativity difference to identify the type of bond between the following:
nonpolar covalent (NP), polar covalent (P), or
ionic (I).
A. K-N 2.2 ionic (I)
B. N-O polar covalent (P)
C. Cl-Cl 0.0 nonpolar covalent (NP)
D. H-Cl 0.9 polar covalent (P)

12. Covalent Bonding -- Polar Bonds and Molecules --
Bond Polarity
“The Tug of War”
The pairs of electrons that are bonds between atoms are pulled between the nuclei of the atoms in a bond.
The electronegativities of the atoms determine the winner.
Classifications for Bonds
Nonpolar covalent
When atoms pull the bond equally
Happens with two atoms of equal electronegativity, most often using the same atoms
Examples: H2, O2, N2
Polar covalent
When atoms pull the bond unequally
Happens with two atoms of different electronegativities
Example: HCl, HF, NH

13. Covalent Bonding -- Polar Bonds and Molecules --
In a polar molecule, one end of the molecule is slightly more electronegative than the other atom, resulting in one atom being slightly negative (-) because of higher electronegativitiy, and the other atom being slightly positive (+) because of lower electronegativity.
 is known as a partial charge since it is much less than 1+ or 1- charge.
You can draw the polarity (direction of the pull) on the atom.