Chapter 8 Covalent Bonding 8.3 Bonding Theories 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.

What is the problem with a flat 2-dimensional map? CHEMISTRY & YOU What is the problem with a flat 2-dimensional map? It does not show an accurate picture of what is really going on or what something truly looks like. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

VSEPR Theory What do scientists use the VSEPR theory for? VSEPR Theory Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

VSEPR Theory To explain the three-dimensional shape of molecules, scientists use Valence-Shell Electron-Pair Repulsion theory (VSEPR theory). VSEPR theory states that the repulsion between electron pairs causes molecular shapes to adjust so that the valence electron-pairs stay as far apart as possible. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

(electron dot structure) VSEPR Theory The structural formula and electron dot structure of methane (CH4) show the molecule as if it were flat and two-dimensional. They fail to reflect the true three-dimensional shape of the molecule. Methane (electron dot structure) (structural formula) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

All of the H–C–H angles are 109.5°, the tetrahedral angle. VSEPR Theory In methane, the hydrogen atoms are at the four corners of a geometric shape called a tetrahedron. All of the H–C–H angles are 109.5°, the tetrahedral angle. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

In ammonia (NH3) one of the pairs of electrons are unshared. VSEPR Theory Unshared (lone) pairs of electrons are also important in predicting the shapes of molecules. Ammonia (NH3) In ammonia (NH3) one of the pairs of electrons are unshared. Nonbinding pairs repel electrons more than shared pairs. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

VSEPR Theory Because no atom needs these electrons; they are held closer than bonding pairs. The lone pair pushes the bonding pairs closer together changing the angle and shape. The H—N—H bond angle is only 107°, rather than the tetrahedral angle of 109.5°. Unshared electron pair 107° Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Thus, the water molecule is bent but flat VSEPR Theory Water’s two lone pairs of electrons push the bonding pairs father around the central oxygen. Thus, the water molecule is bent but flat With two unshared pairs, the H—O—H bond angle is compressed to about 105°. Unshared pairs 105° Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Thus, CO2 is a linear molecule. VSEPR Theory The carbon in a carbon dioxide molecule has no unshared electron pairs. The double bonds joining the oxygens to the carbon are farthest apart and the O=C=O bond angle is 180°. Thus, CO2 is a linear molecule. Carbon dioxide (CO2) No unshared electron pairs on carbon 180° Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Here are some common molecular shapes. VSEPR Theory Here are some common molecular shapes. Linear Trigonal planar Bent Pyramidal Tetrahedral Trigonal bipyramidal Octahedral Square planar Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

What causes valence electron-pairs to stay as far apart as possible? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

What causes valence electron-pairs to stay as far apart as possible? The repulsion between electron pairs due to their negative charges causes valence electron-pairs to stay as far apart as possible. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecular Orbitals How are atomic and molecular orbitals related? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecular Orbitals Just as an atomic orbital belongs to a particular atom, a molecular orbital belongs to a molecule as a whole. A molecular orbital that can be occupied by two electrons of a covalent bond is called a bonding orbital. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecular Orbitals When two atoms combine, their atomic orbitals overlap to produce molecular orbitals, or orbitals that apply to the entire molecule. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecular Orbitals Covalent bonding results from an imbalance between the attractions and repulsions of the nuclei and electrons involved. The nuclei and electrons attract each other. Nuclei repel other nuclei. Electrons repel other electrons. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

The result is a stable diatomic molecule. Molecular Orbitals In a bonding molecular orbital, the attractions between the nuclei and the electrons are stronger than the repulsions. The balance of all the interactions between the atoms is thus tipped in favor of holding the atoms together. The result is a stable diatomic molecule. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Its symbol is the Greek letter sigma (σ). Molecular Orbitals Sigma Bonds When a molecular orbital forms that is symmetrical around the axis connecting two atomic nuclei, a sigma bond molecular orbital is formed. Its symbol is the Greek letter sigma (σ). s atomic orbital Bond axis Sigma-bonding molecular orbital  represents the nucleus Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecular Orbitals Sigma Bonds Just like s orbitals, p orbitals can also overlap to form molecular orbitals. When two fluorine atoms combine, the p orbitals overlap end to end to produce a bonding molecular orbital. The result is a sigma bond by the p atomic orbitals. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecular Orbitals Sigma Bonds There is a high probability of finding a pair of electrons between the positively charged nuclei of a sigma bond. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecular Orbitals Pi Bonds The side-by-side overlap of p orbitals produces what is called a pi bond molecular orbital. Its symbol is the Greek letter pi (). p atomic orbital Pi-bonding molecular orbital  represents the nucleus Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecular Orbitals Pi Bonds In a pi bond, the bonding electrons are most likely to be found in sausage-shaped regions above and below the bond axis of the bonded atoms. Because orbitals in pi bonding overlap less than in sigma bonding, pi bonds tend to be weaker than sigma bonds. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

In these drawings, show where an electron is most likely to be found? Sigma Pi Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

In these drawings, show where an electron is most likely to be found? Sigma Pi Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Hybrid Orbitals What is orbital hybridization? Hybrid Orbitals Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Hybrid Orbitals Orbital hybridization is the combining of two different types of atomic orbitals. In hybridization, several atomic orbitals mix to form the same total number of equivalent hybrid orbitals. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Hybridization of Orbitals Hybrid Orbitals Hybridization of Orbitals Recall that the carbon atom promotes one of the 2s electrons to a 2p orbital to give it four bonding sites. This creates four sp3 hybrid orbitals. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

S F F Hybridization of Orbitals Hybrid Orbitals Hybridization of Orbitals Sulfur has 6 valence electrons leaving room for 2 flourine atoms to combine creating a SF2 molecule. So why do we get SF6? S F F Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Hybrid Orbitals Hybridization of Orbitals Hybridization of orbitals helps explain why some atoms can violate the octet rule. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

How many hybridized orbitals form when one 2s orbital is hybridized with two 2p orbitals? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

How many hybridized orbitals form when one 2s orbital is hybridized with two 2p orbitals? Three sp2 orbitals form. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Orbital hybridization provides for the expansion of the octet rule. Key Concepts Just as an atomic orbital belongs to a particular atom, a molecular orbital belongs to a molecule as a whole. In order to explain the three-dimensional shape of molecules, scientists use the valence-shell electron-pair repulsion theory (VSEPR theory). Orbital hybridization provides for the expansion of the octet rule. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

END OF 8.3 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.