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.

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

In reality, methane molecules are three-dimensional. VSEPR Theory In reality, methane molecules are three-dimensional. The hydrogens in a methane molecule are at the four corners of a geometric solid called a regular tetrahedron. In this arrangement, all of the H–C–H angles are 109.5°, the tetrahedral angle. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

VSEPR Theory In order 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.

However, one of the valence-electron pairs is an unshared pair. VSEPR Theory Unshared pairs of electrons are also important in predicting the shapes of molecules. The nitrogen in ammonia (NH3) is surrounded by four pairs of valence electrons. However, one of the valence-electron pairs is an unshared pair. Ammonia (NH3) 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.

Animated molecular geometries http://intro. chem. okstate Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

VSEPR Theory Go online to find THREE examples of molecules that represent the 8 molecular shapes. Make a display of your product. Molecular geometry Linear Trigonal planar Bent Pyramidal Tetrahedral Trigonal bipyramidal Octahedral Square planar Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

example Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Grading Rubric Task points Student collected 24 points 3 examples for each Shape Students drew and 24 point Labelled each example Quality of work: excellent 6 points good 4 points careless 0 points Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Hybrid Orbitals The VSEPR theory works well when accounting for molecular shapes, but it does not help much in describing the types of bonds formed. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Hybrid Orbitals Orbital hybridization provides information about both molecular bonding and molecular shape. 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.

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 information about both molecular bonding and molecular shape. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

molecular orbital: an orbital that applies to the entire molecule Glossary Terms molecular orbital: an orbital that applies to the entire molecule bonding orbital: a molecular orbital that can be occupied by two electrons of a covalent bond sigma bond ( bond): a bond formed when two atomic orbitals combine to form a molecular orbital that is symmetrical around the axis connecting the two atomic nuclei pi bond ( bond): a covalent bond in which the bonding electrons are most likely to be found in sausage-shaped regions above and below the bond axis of the bonded atoms Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Glossary Terms tetrahedral angle: a bond angle of 109.5° that results when a central atom forms four bonds directed toward the center of a regular tetrahedron VSEPR theory: valence-shell electron-pair repulsion theory; because electron pairs repel, molecules adjust their shapes so that valence electron pairs are as far apart as possible hybridization: the mixing of several atomic orbitals to form the same total number of equivalent hybrid orbitals Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.