Transcript vsepr ppt
Chemical Bonding II: Molecular Geometry and Hybridization of Atomic Orbitals 10.1 Valence shell electron pair repulsion (VSEPR) model: Predict the geometry of the molecule from the electrostatic repulsions between the electron (bonding and nonbonding) pairs. Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry AB2 2 0 linear linear B B 10.1 Cl Be Cl lone pairs on to central atom 20 atoms bonded central atom 10.1 VSEPR Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry AB2 2 0 linear linear 0 trigonal planar trigonal planar AB3 3 10.1 10.1 VSEPR Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry AB2 2 0 linear linear trigonal planar tetrahedral AB3 3 0 trigonal planar AB4 4 0 tetrahedral 10.1 10.1 VSEPR Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry AB2 2 0 linear linear trigonal planar AB3 3 0 trigonal planar AB4 4 0 tetrahedral tetrahedral AB5 5 0 trigonal bipyramidal trigonal bipyramidal 10.1 10.1 VSEPR Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry AB2 2 0 linear linear trigonal planar AB3 3 0 trigonal planar AB4 4 0 tetrahedral tetrahedral AB5 5 0 trigonal bipyramidal trigonal bipyramidal AB6 6 0 octahedral octahedral 10.1 10.1 10.1 lone-pair vs. lone pair lone-pair vs. bonding bonding-pair vs. bonding > > repulsion pair repulsion pair repulsion VSEPR Class # of atoms bonded to central atom # lone pairs on central atom AB3 3 0 AB2E 2 1 Arrangement of electron pairs Molecular Geometry trigonal planar trigonal planar trigonal planar bent 10.1 VSEPR Class # of atoms bonded to central atom # lone pairs on central atom AB4 4 0 AB3E 3 1 Arrangement of electron pairs Molecular Geometry tetrahedral tetrahedral tetrahedral trigonal pyramidal 10.1 VSEPR Class # of atoms bonded to central atom # lone pairs on central atom AB4 4 0 Arrangement of electron pairs Molecular Geometry tetrahedral tetrahedral AB3E 3 1 tetrahedral trigonal pyramidal AB2E2 2 2 tetrahedral bent O H H 10.1 VSEPR Class AB5 AB4E # of atoms bonded to central atom 5 4 # lone pairs on central atom Arrangement of electron pairs Molecular Geometry 0 trigonal bipyramidal trigonal bipyramidal 1 trigonal bipyramidal See-Saw (distorted tetrahedron) 10.1 VSEPR Class AB5 # of atoms bonded to central atom 5 # lone pairs on central atom 0 AB4E 4 1 AB3E2 3 2 Arrangement of electron pairs Molecular Geometry trigonal bipyramidal trigonal bipyramidal trigonal bipyramidal trigonal bipyramidal See-Saw T-shaped F F Cl F 10.1 VSEPR Class AB5 # of atoms bonded to central atom 5 # lone pairs on central atom 0 AB4E 4 1 AB3E2 3 2 AB2E3 2 3 Arrangement of electron pairs Molecular Geometry trigonal bipyramidal trigonal bipyramidal trigonal bipyramidal trigonal bipyramidal See-Saw trigonal bipyramidal T-shaped linear I I I 10.1 VSEPR Class # of atoms bonded to central atom # lone pairs on central atom AB6 6 0 octahedral octahedral AB5E 5 1 octahedral square pyramidal F F F Arrangement of electron pairs Molecular Geometry Br F F 10.1 VSEPR Class # of atoms bonded to central atom # lone pairs on central atom AB6 6 0 octahedral octahedral AB5E 5 1 octahedral AB4E2 4 2 octahedral square pyramidal square planar Arrangement of electron pairs Molecular Geometry F F Xe F F 10.1 10.1 Predicting Molecular Geometry 1. Draw Lewis structure for molecule. 2. Count number of lone pairs on the central atom and number of atoms bonded to the central atom. 3. Use VSEPR to predict the geometry of the molecule. What are the molecular geometries of SO2 and SF4? (In SF4, S uses an expanded octet of 10.) F S S F S F AB2E bent AB4E F See-Saw (distorted Tetrahedron) 10.1 Parent shapes for EXn molecules (n = 2-5) shape EX2 n 2 EX3 3 trigonal planar EX4 4 tetrahedral EX5 5 trigonal Formula shapes of structures linear bipyramidal Parent shapes for EXn molecules (n = 6-8) EX6 n 6 EX7 7 pentagonal bipyramidal EX8 8 square antiprismatic Formula shape octahedral shapes of structures Final structures for VSEPR theory. More final structures for VSEPR. Dipole Moments and Polar Molecules electron poor region electron rich region H F d+ d- 10.2 10.2 Which of the following molecules have a dipole moment? H2O, CO2, SO2, and CH4 O S dipole moment polar molecule dipole moment polar molecule H O C O no dipole moment nonpolar molecule H C H H no dipole moment nonpolar molecule 10.2 Chemistry In Action: Microwave Ovens 10.2 How does Lewis theory explain the bonds in H2 and F2? Sharing of two electrons between the two atoms. Overlap Of Bond Dissociation Energy Bond Length H2 436.4 kJ/mole 74 pm 2 1s F2 150.6 kJ/mole 142 pm 2 2p Valence bond theory – bonds are formed by sharing of e- from overlapping atomic orbitals. 10.3 Stop here Hybridization – mixing of two or more atomic orbitals to form a new set of hybrid orbitals. 1. Mix at least 2 nonequivalent atomic orbitals (e.g. s and p). Hybrid orbitals have very different shape from original atomic orbitals. 2. Number of hybrid orbitals is equal to number of pure atomic orbitals used in the hybridization process. 3. Covalent bonds are formed by: a. Overlap of hybrid orbitals with atomic orbitals b. Overlap of hybrid orbitals with other hybrid orbitals 10.4 10.4 Formation of sp2 Hybrid Orbitals 10.4 Formation of sp Hybrid Orbitals 10.4 How do I predict the hybridization of the central atom? Count the number of lone pairs AND the number of atoms bonded to the central atom # of Lone Pairs + # of Bonded Atoms Hybridization Examples 2 sp BeCl2 3 sp2 BF3 4 sp3 CH4, NH3, H2O 5 sp3d PCl5 6 sp3d2 SF6 10.4 10.4 Sigma (s) and Pi Bonds (p) 1 sigma bond Single bond Double bond 1 sigma bond and 1 pi bond Triple bond 1 sigma bond and 2 pi bonds How many s and p bonds are in the acetic acid (vinegar) molecule CH3COOH? H C O H C O H s bonds = 6 + 1 = 7 p bonds = 1 H 10.5 Pi bond (p) – electron density above and below plane of nuclei Sigma bond (s) – electron density between the 2 atoms of the bonding atoms 10.5 10.5 10.5 O O Experiments show O2 is paramagnetic (has UNPAIRED e-) No unpaired e- Should be diamagnetic MO Theory is NOT in the AP Chemistry Curriculum and will NOT be on the AP exam! This is just a quick overview! Molecular orbital theory – bonds are formed from interaction of atomic orbitals to form molecular orbitals. 10.6 Energy levels of bonding and antibonding molecular orbitals in hydrogen (H2). A bonding molecular orbital has lower energy and greater stability than the atomic orbitals from which it was formed. An antibonding molecular orbital has higher energy and lower stability than the atomic orbitals from which it was formed. 10.6 10.6 Molecular Orbital (MO) Configurations 1. The number of molecular orbitals (MOs) formed is always equal to the number of atomic orbitals combined. 2. The more stable the bonding MO, the less stable the corresponding antibonding MO. 3. The filling of MOs proceeds from low to high energies. 4. Each MO can accommodate up to two electrons. 5. Use Hund’s rule when adding electrons to MOs of the same energy. 6. The number of electrons in the MOs is equal to the sum of all the electrons on the bonding atoms. 10.7 1 bond order = 2 bond order ½ ( Number of electrons in bonding MOs 1 - ½ Number of electrons in antibonding MOs ) 0 10.7 Delocalized molecular orbitals are not confined between two adjacent bonding atoms, but actually extend over three or more atoms. 10.8 10.6