8.3 Bonding Theories > 1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Chapter 8 Covalent Bonding 8.1 Molecular Compounds

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Chapter 8Covalent Bonding

8.1 Molecular Compounds8.2 The Nature of Covalent Bonding

8.3 Bonding Theories

8.4 Polar Bonds and Molecules



• 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.

VSEPR TheoryVSEPR Theory

Methane(electron dot structure)

Methane(structural formula)



• 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.




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.




• 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)



Here are some common molecular shapes.


Linear Trigonal planar Bent Pyramidal

Tetrahedral Trigonalbipyramidal

Octahedral Square planar


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Animated molecular geometries

http://intro.chem.okstate.edu/1314F00/Lecture/Chapter10/VSEPR.html

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Go online to find THREE examples of molecules that represent the 8 molecular shapes. Make a display of your product.

Molecular geometry

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Linear Trigonal planar Bent Pyramidal

Tetrahedral Trigonalbipyramidal

Octahedral Square planar


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exampleexample



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Grading RubricGrading 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




The VSEPR theory works well when accounting for molecular shapes, but it does not help much in describing the types of bonds formed.

Hybrid OrbitalsHybrid 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.

Hybrid OrbitalsHybrid Orbitals



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.

Key ConceptsKey Concepts



• 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

Glossary TermsGlossary 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

Glossary TermsGlossary Terms

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8.3 Bonding Theories > 1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Chapter 8 Covalent Bonding 8.1 Molecular Compounds