Chemistry 8.3 Bonding Theories 8.3

• This car is being painted by a process called electrostatic spray painting. The negatively charged droplets are attracted to the auto body. You will learn how attractive and repulsive forces influence the shapes of molecules.

8.3

8.3 • Molecular Orbitals

– How are atomic and molecular orbitals related?

8.3 • molecular orbitals

– When two atoms combine – the molecular orbital model assumes that their atomic

orbitals overlap – produce orbitals that apply to the entire molecule.

8.3 – atomic orbital belongs to a particular atom – molecular orbital belongs to a molecule as a whole. – bonding orbital

• A molecular orbital that can be occupied by two electrons of a covalent bond.

8.3 – Sigma Bonds

• sigma bond – When two atomic orbitals combine to form a molecular

orbital that is symmetrical around the axis connecting two atomic nuclei

8.3

• A Sigma Bond

8.3 • When two fluorine atoms combine • the p orbitals overlap to produce a bonding molecular

orbital • The F—F bond is a sigma bond.

8.3 Molecular Orbitals

– Pi Bonds • In a pi bond (symbolized by the Greek letter π), the

bonding electrons are most likely to be found in sausage-shaped regions above and below the bond axis of the bonded atoms.

8.3 Molecular Orbitals

• Pi-bonding Molecular Orbital

8.3 • VSEPR Theory

– How does VSEPR theory help predict the shapes of molecules?

8.3 • The hydrogens in a methane molecule are at the four

corners of a geometric solid. • All of the H—C—H angles are 109.5°, the tetrahedral

angle.

8.3 • VSEPR theory

– The valence-shell electron-pair repulsion theory – explains the three-dimensional shape of methane.

8.3 – According to VSEPR theory:

• the repulsion between electron pairs causes molecular shapes to adjust so that the valence-electron pairs stay as far apart as possible.

8.3 • The measured H—N—H bond angle is only 107°.

8.3 • The measured bond angle in water is about 105°.

8.3 • The carbon dioxide molecule is linear.

8.3

• Nine Possible Molecular Shapes

8.3 • Hybrid Orbitals

– In what ways is orbital hybridization useful in describing molecules?

• Orbital hybridization provides information about both molecular bonding and molecular shape.

• Hybridization – several atomic orbitals mix to form the same total

number of equivalent hybrid orbitals.

8.3 – Hybridization Involving Single Bonds

8.3 – Hybridization Involving Double Bonds

8.3 – Hybridization Involving Triple Bonds

Quiz.

1. A molecular orbital belongs to a A. specific atom. B. molecule as a whole. C. specific pair of atoms. D. central atom.

2. VSEPR theory enables prediction of 3-dimensional molecular shape because the valence electron pairs

A. are attracted to each other. B. form molecules with only four possible shapes. C. stay as far apart as possible. D. always form tetrahedral shapes.

3. Orbital hybridization provides information about A. both molecular bonding and molecular shape. B. both molecular bonding and bond energy. C. neither molecular bonding nor molecular shape. D. neither molecular bonding nor bond energy.

END