Hybridization and Bonding.pdf

Unit 2: Structure and Properties HYBRIDIZATION OF ORBITALS AND BONDING Put on your 3-D glasses! Rationale for hybridization  Experimentally we know the bond angles (109.5º).  But our current understanding of orbitals doesn’t allow us to achieve these bond angles. Types of Bonds...

Unit 2: Structure and Properties HYBRIDIZATION OF ORBITALS AND BONDING Put on your 3-D glasses! Rationale for hybridization  Experimentally we know the bond angles (109.5º).  But our current understanding of orbitals doesn’t allow us to achieve these bond angles. Types of Bonds  Sigma (σ) bonds  End-to-end bonding  There is an overlap  One in every type of bond  Pi (π) bonds  Side-to-side bonding of unhybridized p- orbitals  There is no overlap  There is one pi bond in a double bond  There are two pi bonds in a triple bond Single bond [Sigma (σ) bonds] More sigma bonds! Double bonds Consist of one sigma bond and one pi bond Form from the side to side bonding of unhybridized p-orbitals Double bond of ethene Triple bonds Consist of one sigma bond and two pi bonds  Hybridization  Uses modifications of molecular models to account for observed structures of molecules or ions  Is a mixing of the native atomic orbitals to form special hybrid orbitals for bonding  The special orbitals will then strive to be as far away from each other in space as they can be Types of Hybridization  sp3  sp2  sp  dsp3  d2sp3 sp3 hybridization  Native s orbital x z y  Native p orbitals x z y x px z y x py z y pz  Hybrid sp3 orbitals x z x y z y x x z z y y  Hybrid sp3 orbitals x z y  Hybrid sp3 orbitals x z y sp3 orbitals 4 effective pairs 109.5°, 107.3°(w/1 lone pair), or 104.5° (w/2 lone pairs) tetrahedral, pyramidal, or bent  Hybrid sp3 orbitals overlapping orbitals H x C H H z H CH4 y 4 σ bonds in the molecule sp3 hybridization –Methane 20 Orbital picture and structure of methane 21 sp3 Hybridization  Molecules that have tetrahedral geometry like CH4, NH3, H2O, SO42-, and ClO3- exhibit sp3 hybridization on the central atom. Methane with Hybridized Orbitals  Overlap of the Hydrogen 1s orbitals with the hybridized sp3 orbitals from the central Carbon. sp2 hybridization  Native s orbital x z y  Native p orbitals x z y x px z y x Leave this one as is py z y pz  Hybrid sp2 orbitals x z x y x z y z y  Hybrid sp2 orbitals x z y sp2 orbitals 3 effective pairs 120° trigonal planar  Hybrid sp2 orbitals Remember the un- hybridized p orbital? x z y sp2 orbitals 3 effective pairs 120° trigonal planar  Hybrid sp2 orbitals overlapping orbitals side-by-side orbitals H H x x C C H H z z 5 σ bonds C2H4 y y 1 π bond in molecule sp2 hybridization Ethene 31 Orbital picture of ethylene 32 Trigonal Planar – sp2 Hybridization  Molecules with trigonal planar geometry like SO3, C2H4, SeS2, CO32-, exhibit sp2 hybridization on the central atom. Hybridized and Unhybridized Orbital View Side view Bonding and hybridized orbitals  Hybridized orbitals make sigma bonds  Unhybridized orbitals make pi bonds sp hybridization  Native s orbital x z y  Native p orbitals x z y x px z y x Leave this one as is py z y Leave this one as is pz  Hybrid sp orbitals x x z z y y  Hybrid sp orbitals x z sp orbitals 2 effective pairs y 180° linear  Hybrid sp orbitals Remember the un- hybridized p orbitals? x z sp orbitals 2 effective pairs y 180° linear  Hybrid sp orbitals x H x C C H z z y y C2H2  Hybrid sp orbitals overlapping orbitals side-by-side orbitals x x z z y y C2H2 sp hybridization – Ethyne 45 Orbital picture of ethyne 46 sp hybridization  Molecules that have a linear geometry like CO2, N2O, BeH2, HCN, C2H2 all exhibit sp hybrization on the central atom. CO2 Structure sp hybridization Pi bonds and Sigma Bonds  CO2 exhibits sp hybridization on the C and sp2 hybridization on the Oxygens. N2 Hybridization  Diatomic Nitrogen has a Lewis structure showing a triple bond. Hybridized Orbitals When Exceeding the Octet Rule PCl5 dsp3 Hybridized  Trigonal bipyramid geometry  SeF4, PCl5, BrF3, XeCl2 Octahedral Geometry  d2sp3 hybridization  XeF4, BrCl5, SeI6 Delocalization of Electrons  In molecules that show resonance structures, we have a delocalization of electrons.  The available unhybridized p orbitals all overlap and stabilize the structure through the π interactions. VSEPR Theory (1957; Ronald Gillespie, McMaster University, Hamilton, Ontario)  Valence Shell Electron Pair Repulsion  Each pair of electrons (whether in a bond or lone pairs) repel each other.  Repulsion forces will maximize the distance between electron pairs until repulsion is minimized.  The resulting 3-D arrangement of valence e- pairs around central atom will determine the shape.  Carbon Dioxide, CO2 1. Central atom = C 4 e- O 6 e- X 2 O’s = 12 e- 2. Valence electrons = Total: 16 valence electrons 3. Form bonds. This leaves 12 electrons (6 pair). 4. Place lone pairs on outer atoms. 5. Check to see that all atoms have 8 electrons around it except for H, which can have 2.  Carbon Dioxide, CO2 C 4 e- O 6 e- X 2 O’s = 12 e- Total: 16 valence electrons How many are in the drawing? 6. There are too many electrons in our drawing. We must form DOUBLE BONDS between C and O. Instead of sharing only 1 pair, a double bond shares 2 pairs. So one pair is taken away from each atom and replaced with another bond.  H2CO Double and even triple bonds are commonly observed for C, N, P, O, and S SO3 C2F4 MOLECULAR GEOMETRY  MOLECULAR GEOMETRY Molecule adopts the shape that minimizes the electron pair repulsions. VSEPR  Valence Shell Electron Pair Repulsion theory.  Most important factor in determining geometry is relative repulsion between electron pairs.  Some Common Geometries Linear Trigonal Planar Tetrahedral Hybridization and molecular shapes of some molecules involving sporbitals 64 Geometry of molecules containing one or more lone pairs in central atom 65 THANK YOU FOR YOUR KIND ATTENTION ! Questions?