Chapter 9 Molecular Geometry

Molecular Shapes Lewis Structures do not account for shape of molecules rather they only show the number and types of bonds between atoms

Molecular Shapes The overall shape is determined by the bond angle, the angle made by the lines joining the nuclei of the atoms in a molecule

Molecular Shapes We will focus on atoms with ABn format, a central atom A has n B atoms bonded to it

VSEPR Model An electron domain consists of nonbonding pairs, single bonds, or multiple bonds

VSEPR Model

VSEPR Model Electron domains are negatively charged, so they repel each other, and stay out of each other’s way

VSEPR Model the best arrangement of a given number of electron domains is the one that minimizes the repulsions among them

VSEPR Model The shape of the substance in the ABn format depends on the number of electron domains surrounding the central atom (Electron-domain geometry)

VSEPR Model Molecular shape describes the arrangement of atoms, not the electron domains (molecular geometry)

VSEPR Model To Predict Shapes: 1. Draw Lewis structure and count e-d 2. Determine e-d geometry 3. Predict molecular geometry

VSEPR Model See table

VSEPR Model

Basic Geometry 0 lone pairs 1 lone pair 2 lone pairs 3 lone pairs Domains Basic Geometry 0 lone pairs 1 lone pair 2 lone pairs 3 lone pairs 2 Linear   3 trigonal planar bent 4 tetrahedral trigonal pyramidal 5 trigonal bipyramidal seesaw T-shaped linear 6 octahedral square pyramidal square planar 15

VSEPR Model

Sample Ex. 8.1-8.2 Use VSEPR to predict shape for the following substances: O3 SnCl3- SeCl2 CO32- IF5 ClF3 ICl4-

VSEPR Model video

VSEPR Model Nonbonding Electrons and Multiple Bonds can affect bond angles

VSEPR Model E-ds for nonbonding electron pairs exert greater repulsive forces on adjacent e-ds and thus tend to compress bond angles

VSEPR Model

VSEPR Model Electron domains for multiple bonds exert a greater repulsive force on adjacent electron domains than single bonds

VSEPR Model

VSEPR Model VSEPR can be applied to larger molecules as well The shape can be predicted around individual atoms

VSEPR Model

VSEPR Model

VSEPR Model

Sample Exercise 9.3 Predicting Bond Angles Predict the approximate values for the H—O—C and O—C—C bond angles in vinyl alcohol .

Bond Polarity a measure of how equally electrons in a bond are shared based on electronegativity

Dipole moment a measure of the charge separation in a molecule

Dipole moment For a molecule with more than 2 atoms, the dipole moment depends on both polarities of the bonds and the geometry of the molecule.

Dipole moment For ABn molecules in which all the B atoms are the same, certain symmetrical shapes will lead to nonpolar molecules even though the individual bonds are polar

Dipole moment Nonpolar symmetrical shapes are linear, trigonal planar, tetrahedral, square planar, trigonal bipyramidal, and octahedral

Dipole moment

Dipole moment

Dipole moment

Sample Exercise 9.4 Polarity of Molecules Predict whether the following molecules are polar or nonpolar: (a) BrCl (b) SO2 (c) SF6 (d) NF3 (e) BCl3

Hybrid orbitals Hybridization is a process that occurs when atomic orbitals mix to form new orbitals called hybrid orbitals and form bonds

Hybrid orbitals

Hybrid orbitals

Predicting hybridization 1. Draw lewis structure 2. Determine # e-d 3. Specify the hybrid orbitals needed to accommodate the electron pairs based on their geometric arrangement

Predicting hybridization # e-d hybridization 2 sp 3 sp2 4 sp3 5 dsp3 6 d2sp3

Sample Exercise 9.5 Hybridization Indicate the hybridization of orbitals employed by the central atom in (a) NH2– (b) SF4 (c) SO32– (d) SF6

Multiple Bonds All of the single bonds we have looked at are called sigma (s) bonds, where there is an overlap in the middle of the region of s and p orbital

Multiple Bonds To describe multiple bonds, we must look at the side to side overlapping of 2 p orbitals, called a pi (p) bond

Multiple Bonds A double bond is one s bond and one p bond

Multiple Bonds A triple bond is one s bond and two p bonds

Multiple Bonds

Multiple Bonds When looking at molecules that exhibit resonance there is delocalized p bonding

Sample Exercise 9.6 Describing  and  Bonds in a Molecule Formaldehyde also known as ? has the following Lewis structure Count the  and  bonds. .

Tell me everything you can about Acetonitrile

Review PF5

Review CO2

Review ICl4-

Review AsH3

Review I3-

Review SO2

Review IF5

Review CO32-

Review SF6

Review ClO4-

Review OF2

Review IF4+

Review ClF3

Review NCS-

Review Methanoic acid Methyl Amine Ethyne Directions: Predict the molecular geometry, bond angle, hybridization, s and p bonds, and polar/nonpolar for the following molecule : Methanoic acid Methyl Amine Ethyne