Chapter Seven Molecular Geometry & Bonding Themes

Section 7.1 Molecular Geometry

What is molecular geometry? Shapes of molecules (molecules actually have 3D structures that affect how they bond in reactions) Based on electrons and their repulsion from each other Valence Shell Electron Pair Repulsion (VSEPR) Focused on general model ABx A = central atom, B = terminal (attached) atoms

Electron Domains & VSEPR Recall: Electron Pairs can be bonding pairs or lone pairs Bonding pairs may be single bonds or multiple bonds An electron domain is a lone pair or a bonded pair (double and triple bonds only count for ONE electron domain)

Electron Domains & VSEPR How many electron domains do these molecules have?

Electron Domain Geometry Geometric shapes based on electron domains AB2 Linear 180° (provided no lone pairs on central) Ex: CO2 AB3 Trigonal Planar 120° (provided no lone pairs on central) Ex: BF3

Electron Domain Geometry Geometric shapes based on electron domains AB4 Tetrahedral 109.5° (provided no lone pairs on central) Ex: CH4 AB5 Trigonal Bipyramidal 120° (equatorial atoms) & 90° (axial atoms) Ex: PCl5

Electron Domain Geometry Geometric shapes based on electron domains AB6 Octahedral 90° between all atoms (provided no lone pairs on central) Ex: SF6

Drawing 3D structures on paper It is helpful to draw molecules on paper with 3-Dimensionality to better visualize the shape

Visualizing it! http://phet.colorado.edu/en/simulation/molecule-shapes

Electron Domain Geometry vs. Molecular Geometry Electron Domain: based on electron domains (bonded and unbonded) Basically, it looks at ALL the electrons Molecular Geometry: based on atoms ONLY (bonded pairs only) Basically only looks at electrons in bonds (or atoms)

Steps for determining geometry Draw Lewis Structure Count electron domains around central atom Determine Electron Domain Geometry Determine Molecular Geometry from atoms only

Electron Domain Geometry vs. Molecular Geometry Consider the following three compounds: CH4, NH3, H2O What are their electron domain geometries? What are their molecular geometries?

Practice Determine what the electron domain geometry and molecular geometry are for the following compounds: SO2 XeF4

Geometry with lone pairs Some electron domains repel MORE than others Lone pairs repel more Because not bonded, they experience less nuclear attraction Double and Triple bonds repel more Due to higher electron density

Geometry with lone pairs

Geometry with lone pairs Other examples

Practice Determine the electron domain geometry and the molecular geometry for the following. Include bond angles as well. SeO2 SF6

Group Quiz #1 State the electron domain geometry, the molecular geometry and the bond angle (if the bond angle is not ideal, state “less than _____°”) PCl3 SeCl4

Molecules with Multiple Central Atoms A central atom is one where it is surrounded by 2 or more atoms Determine the multiple shapes in the molecule around each central atom Ex:

Section 7.2 Molecular Geometry & Polarity

Recalling Polarity Recall: A bond between 2 atoms is polar covalent when difference in electronegativity is greater than 0.5 A molecule OVERALL can also be polar or nonpolar Based on geometry of molecule and Individual bonds in molecule

Some simple examples CO2 and H2O

How to check if molecule is polar First, check if there are lone pairs of electrons If yes, it is POLAR (unless they are “balanced”) If no lone pairs, check if there are polar bonds If there are no polar bonds, is is NON POLAR If there are polar bonds, check for symmetry If all terminal atoms are the same, it is NON POLAR If terminal atoms are not the same, but there is symmetry, it is NON POLAR If terminal atoms are not the same, and there is no symmetry, it is POLAR

Some Examples

Practice Determine if the molecule is POLAR or NON POLAR CH2Cl2 & XeF4 For each hypothetical molecule below, draw one structure that is polar and one that is non polar H2SF4 & H2PCl3

Group Quiz #2 For each molecule below, determine SbCl5 I3- the electron domain geometry, the molecular geometry, draw the 3D-structure on paper, state if it is polar or nonpolar SbCl5 I3-

Section 7.3 Valence Bond Theory

Valence Bond Theory Definition: atoms share electrons when an atomic orbital on one atom overlaps with an atomic orbital on the other

Valence Bond Theory Explains why atoms share electrons Potential energy of resulting molecule is lower than combined energies of isolated atoms A.K.A. when bonds form, energy given off Therefore, energy required to break bonds

Section 7.4 Hybridization of Atomic Orbitals

Hybridization Consider BeCl2 How can it bond with 2 atoms??? Hybridization: mixing of atomic orbitals

Hybridization Hybrid orbitals are always shown in GREEN

Hybridization Consider BF3

Hybridization Consider CH4

Hybridization Consider PCl5

Hybridization Consider SF6

Steps for Hybridization Draw Lewis Structure Count # of electron domains (this is # of hybrid orbitals needed) Determine the hybrid orbital needed Draw ground state configuration of central atom Place electrons in the hybrid orbitals one at a time

Examples Use hybrid orbital theory to explain the bonding in BrF5

Group Quiz #3 Show the hybridization of the following molecule. Be sure to include a) what type of hybrid orbital is needed and 2) the orbital diagram of the hybrid orbital XeF4

Section 7.5 Hybridization in Molecules Containing Multiple Bonds

Hybridization with Multiple Bonds How many electron domains around the carbons? What hybrid orbitals are needed?

Hybridization with Multiple Bonds Bonds that are made using hybrid orbitals (or along the internuclear axis) are called sigma (σ) bonds Bonds that are made using remaining p orbitals and overlap on the sides are called pi (π) bonds

Hybridization with Multiple Bonds

Hybridization with Multiple Bonds