Theories of Bonding & Structure Review Chapter 10: Theories of Bonding & Structure Chemistry: The Molecular Nature of Matter, 6th edition By Jesperson, Brady, & Hyslop

Chapter 10 Concepts VESPR theory Predict molecular geometry & overall dipole moment Valence Bond Theory Identify & draw hybridization of orbitals at central atom Identify & draw σ and π bonds Molecular Orbital Theory Draw MO Energy Diagrams to identify Bond Order Number of Unpaired Electrons

Memorize Linear Trigonal Planar Trigonal Bipyramidal Tetrahedral Planar Triangular Trigonal Bipyramidal Tetrahedral Octahedral

Distorted Tetrahedron Memorize T-shaped Square Pyramid Planar Trigonal Pyramidal Bent Seesaw or Distorted Tetrahedron

Determining 3-D VESPR Stuctures 1. Draw Lewis Structure of Molecule Don't need to compute formal charge If several resonance structures exist, pick only one 2. Count electron pair domains Lone pairs and bond pairs around central atom Multiple bonds count as one set (or one effective pair) 3. Arrange electron pair domains to minimize repulsions Lone pairs Require more space than bonding pairs May slightly distort bond angles from those predicted. In trigonal bipyramid lone pairs are equatorial In octahedron lone pairs are axial Name molecular structure by position of atoms—only bonding electrons

Polarity If symmetrical polar bonds around a central atom then they cancel and there is no overall dipole moment. Molecule is usually polar if All atoms attached to central atom are NOT same, OR There are one or more lone pairs on central atom EXCEPT:

Valence Bond Theory Hybridization = mixing atomic orbitals sp: Linear Individual atoms, each have their own orbitals and orbitals overlap to form bonds. Extent of overlap of atomic orbitals is related to bond strength Hybridization = mixing atomic orbitals sp: Linear sp3d: Trigonal Bipyramidal sp2: Planar Triangular sp3d2: Octahedral sp3: Tetrahedral

Valence Bond Theory Draw lewis dot structure How many lone pairs & bonded atoms will repel one another? That is the number of hybrid orbitals needed 2: sp 3: sp2 4: sp3 5: sp3d 6: sp3d2 Convert the needed number of atomic orbitals into hybridized orbitals. Fill in valence electrons. Remember that any p orbitals will be close enough in energy that they both hybrid & remaining p orbitals will fill half way with electrons before they pair. Draw hybrid orbitals equally spaced around the central atom: Form σ bonds using hybrid orbitals with one electron Hybrid orbitals with two electrons are likely lone pairs If any lone electrons are in p orbitals π bonds will form Describe molecular geometry around central atom(s).

Valence Bond Theory: Example N2 :NN: p p sp E s Hybrid & AO of N AO of N Lone pair and atom bonded to Nitrogen will repel each other. Therefore, need to hybridize 2 orbitals One hybrid orbital with one electron will participate in a σ bond with the other nitrogen The other hybrid orbital contains a lone pair 2 p orbitals each have 1 electron so form 2 π bonds to the other nitrogen

Molecular Orbital Theory Molecular Orbital Theory Views molecule as collection of positively charged nuclei having a set of molecular orbitals that are filled with electrons (similar to filling atomic orbitals with electrons). Doesn't worry about how atoms come together to form molecule

Molecular Orbital Theory O2, F2 and Higher 2p Lower in energy than 2p Li2  N2 2p Lower in energy than 2p Can ignore filled 1s bonding & antibonding and focus on valence electrons

Molecular Orbital Theory: Diagrams σ* π* p π E σ σ* s σ AO of one atom AO of second atom

For the following molecules: Problem Set A For the following molecules: Draw a lewis dot structure. Determine the molecular geometry at each central atom. Identify the bond angles. Identify all polar bonds: δ+ / δ- Assess the polarity of the molecule & indicate the overall dipole moment if one exists AsF5 AsF3 SeO2 GaH3 ICl2- SiO4-4 TeF6

Problem Set B What is the hybridization of oxygen in OCl2? For the species and XeF4O, determine the following: electron domain geometry (geometry including non-bonding pairs) molecular geometry Hybridization around central atom Polarity How many  and  bonds are there in CH2CHCHCH2, and what is the hybridization around the carbon atoms? Draw & list the bonding orbitals for HCN.

What is the bond order & number of unpaired electrons in Problem Set C What is the MO Energy Diagram for B2? How many unpaired electrons does B2 have? What is the bond order & number of unpaired electrons in Draw the MO Energy Diagram for BN.

Problem Set A

Problem Set A

Problem Set A

Problem Set B sp3 XeF4O: octahedral, square pyramid, sp3d2, polar 9, 2, sp2 HCN: C will be create a σ bond to H and N with sp2 hybridized orbitals and use 2 p orbitals to participate in 2 π bonds with N. N will participate in the σ bond with C with an sp2 hybridized orbital, the other will hold the N lone pair, and then N will use 2 p orbitals to π bond with C.

B2 BN MO B2: unpaired e- = 2 O2: BO = 2 unpaired e- = 2 Problem Set C B2 BN σ* σ* π* π* MO B2: unpaired e- = 2 O2: BO = 2 unpaired e- = 2 O2+: BO = 5/2 unpaired e- = 1 O2- : BO = 3/2 unpaired e- = 1 MO BN: σ σ π π σ* σ* σ σ

More Practice Problems: Analyze the following compounds: Draw the lewis dot structure Determine the Geometry using VESPR theory Determine the hybridization at any central atoms using VB Theory Draw & Describe bonding in VB terms: ie # of sigma vs pi bonds H2S SO2 H2C=C=CH2 HCOCl