Chapter 9

CHAPTER 9

Molecular Geometry and Bonding Theories

Katherine Shin & Peedith Maldonado

Dedication PageOur lovely Chemistry teacher,

Ms. Ramona Ricks

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P.S- Give us an A Please.

9.1 Molecular Shapes

The overall shape of a molecule is determined by its bond angles, the angles made by the lines joining the nuclei of the atoms in the molecule.

The possible shapes of Abn molecules depend on the value of “n.”

Examples: AB2 molecule must be either linear or bent

AB3 molecule must be either trigonal planar pr trigonal pyramidal

9.2- The VSEPR Model

A bonding pair of electrons thus defines a region in which the elec-trons will more likely be found. (The region is referred to as electron domain)

Nonbonding pair (lone pair) of electrons defines an electron domain that is located principally on one atom.

THE VSEPR model is based on the idea that electron domains are negatively charged & therefore, repel each other.

-The VSEPR predicts that the best arrangement of electron domains is the one that minimizes the repulsions among them.

Electron domain geometry- The arrangement

Of electron domains about the central atom of a

Molecule or ion.

*Molecular geometry is the arrangement of only

the atoms in a molecule or ion.

By looking at the VSEPR model, we can predict

the electron-domain geometry.

-From knowing how many domains are due to

Nonbonding pairs, we can then predict the

Molecular geometry of a molecule or ion from

Its electron-domain geometry.

Electron domain geome-tries

There are five….

Molecular Geometry

CO2

Linear2 electron do-mains

Molecular Geometry

Trigonal Pla-nar

3 electron do-mains

Trigonal Planar

Bent

BF3NO3

Molecular Geometry

4 electron domainsTetrahe-dral

Tetrahedral

Trigonal Pyramidal

Bent

CH4

NH3

H2O

Molecular Geometry

TrigonalBipyra-midal5 electron do-

mains

Seesaw

TrigonalBipyrami-

dal

T-shaped

Lin-ear

PCl5 SF4

XeF2

ClF3

Molecular Geometry

Octahe-dral

6 electron do-mains

OctahedralSquare

Pyramidal

Square Pla-nar

SF6

BrF5

XeF4

9.3 Molecular Shape & Molecular Polar-ity

For a molecule that consists of more than two atoms, the dipole moment depends on both the polarities of the individual bonds and the geometry of the molecule.

H ClPo-lar

CO ONon-Po-lar

More Exam-ples

9.5 Hybrid Orbitals

Atomic orbitals on an atom mix to form new orbitals called hybrid or-bitals.

The process of mixing atomic orbitals is called hybridization.

Provide a convenient model for using valence-bond theory to describe the covalent bonds in molecules with geometries that conform to the electron domain geometries predicted by the VSEPR model.

Steps that allow us to predict the hybrid orbitals used by an atom in the bonding:

1. Draw the lewis structure for the molecule or ion.

2. Determine the electron-domain geometry using the VSEPR model.

3. Specify the hybrid orbitals needed to accommodate the electron pairs based on their geometric arrangement.

Example:

NH3

QUIZ

Find: molecular formula, electron domain ge-ometry, molecular geometry, number of elec-tron domains(bonding/nonbonding), polarity, bond angles, hybridization

Phosporus hexaflouride (negative one ion)

PF6

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