Chapter 8 Covalent Bonding 8.4 Polar Bonds and Molecules 8.1 Molecular Compounds 8.2 The Nature of Covalent Bonding 8.3 Bonding Theories 8.4 Polar Bonds and Molecules Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Nonpolar Covalent Bond Electrons are shared equally. Bond Polarity Nonpolar Covalent Bond Electrons are shared equally. Polar Covalent Bond Electrons are shared unequally. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Hydrogen Chloride (HCl) Bond Polarity Hydrogen Chloride (HCl) Hydrogen has an electronegativity of 2.1 Chlorine has an electronegativity of 3.0. This covalent bond is polar. Cl acquires a slight negative charge. H acquires a slightly positive charge. δ+ δ– H—Cl Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Hydrogen Chloride (HCl) Bond Polarity Hydrogen Chloride (HCl) Partial charges can be shown as clouds of electron density. They are also represented by an arrow pointing to the more electronegative atom. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Bond Polarity The electronegativity difference between two atoms tells you what kind of bond is likely to form. Electronegativity Differences and Bond Types Electronegativity difference range Most probable type of bond Example 0.0–0.4 Nonpolar covalent H—H (0.0) 0.5–1.0 Moderately polar covalent δ+ δ– H—Cl (0.9) 1.0–1.9 Very polar covalent H—F (1.9) >2.0 Ionic Na+Cl– (2.1) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Sample Problem 8.3 Identifying Bond Type Which type of bond will form between the following pairs of atoms? a. N and H b. F and F c. Ca and Cl d. Na and F Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Sample Problem 8.3 Solve Based on the electronegativity difference, determine the bond type using Table 8.4. a. N(3.0), H(2.1); 0.9; moderately polar covalent b. F(4.0), F(4.0); 0.0; nonpolar covalent c. Ca(1.0), Cl(3.0); 2.0; ionic d. Na(0.9), F(4.0); 1.5; ionic Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Dipole: Molecule that has two poles (electrically charged regions) Bond Polarity Polar Molecule: Molecules in which the electrons are unequally distributed. One end of the molecule is slightly negative and the other end is slightly positive. Dipole: Molecule that has two poles (electrically charged regions) HCl is an example of a dipole Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecule polarity depends on the shape and orientation of the bonds. Bond Polarity Molecule polarity depends on the shape and orientation of the bonds. Nonpolar Polar O C O bond polarities cancel bond polarities do not cancel Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Arrange the following covalent bonds in order of decreasing polarity. H-Cl H-C H-F H-O H-H S-Cl Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Arrange the following covalent bonds in order of decreasing polarity. H-Cl (3.0 – 2.1 = 0.9) H-C (2.5-2.1 = 0.4) H-F (4.0-2.1 = 1.9) H-O (3.5-2.1 = 1.4) H-H (2.1-2.1 = 0) S-Cl (3.0-2.5 = 0.5) c,d,a,f,b,e Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Attractions Between Molecules Intermolecular Forces Weaker than ionic or covalent bonds Types Van der Waals Forces Dipole Interactions Dispersion Forces Hydrogen Bonds Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Attractions Between Molecules Dipole Interactions Polar molecules are attracted to each other Similar to, but much weaker than, ionic bonds. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Attractions Between Molecules Dispersion Forces Weakest of all molecular interactions Caused by the motion of electrons. When electrons happen to be more on one side of a molecule, they influence their neighbor’s electrons Forces increase with number of electrons Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Attractions Between Molecules Dispersion Forces F and Cl have relatively few electrons and are gases at room temperature. Bromine attracts other bromine molecules enough to make it a liquid at room temperature. Iodine is a solid at room temperature. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Attractions Between Molecules Hydrogen bonds - a hydrogen covalently bonded to a very electronegative atom is also weakly bonded to an unshared electron pair of another atom. The other atom may be in the same molecule or in a nearby molecule. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Attractions Between Molecules Hydrogen Bonds The positive region of one water molecule attracts the negative region of another water molecule. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Attractions Between Molecules Hydrogen Bonds A hydrogen bond has about 5 percent of the strength of the average covalent bond. Hydrogen bonds are the strongest of the intermolecular forces. They are extremely important in determining the properties of water and biological molecules. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

END OF 8.4 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.