Chapter 9 Covalent Bonding: Orbitals
Localized electron model A bond is made when a half-filled orbital of one atom overlaps with a half-filled orbital of another.! Bond: orbitals overlap straight on p Bond: orbitals overlap side by side Pairs of atoms form 1! bond and 0, 1 or 2 p bonds.
Possible problem with the idea that bonds come from the overlap of atomic orbitals: Structure of Methane (CH 4 ) vs. 90º 109.5º Atomic orbitals don t seem to provide the required angles for a tetrahedral geometry
carbon Another problem: only two unpaired e- s 2p So should Carbon form! "bonds with 2s only two Hydrogen atoms?
Hybridization of Atomic Orbitals
Hybrid orbitals are atomic orbitals obtained when 2 or more regular orbitals of the same atom combine in preparation to form a covalent bond
Hybridizing Atomic Orbitals hybrid orbitals are used only for atoms in a molecule, not for isolated atoms hybrid orbitals are not s, p, d, or f shaped but are a mash-up of them # of hybrid orbitals = # of atomic orbitals (s,p,d,f) from which they were generated hybridization permits more bonds and stronger bonds covalent bonds in molecules result from the overlap of half-filled hybrid atomic orbitals
Procedure For Hybridizing Atomic Orbitals draw the Lewis structure of the molecule an atom needs one hybrid orbital for each sigma bond and each lone pair or # hybrid orbitals = Steric # (SN)
sp 3 Hybridization
(sp3_hybridization)
sp 3 Hybridization Promote an electron from the 2s to the 2p orbital 2p 2p 2s 2s
sp 3 Hybridization Mix together (hybridize) the 2s orbital and the three 2p orbitals 2p 2 sp 3 2s
sp 3 Hybridization Mix together (hybridize) the 2s orbital and the three 2p orbitals 2 sp 3
Shapes of orbitals s p sp 3
!Bond in CH 4 H C s sp 3! C H H C
Justification for Orbital Hybridization The model is consistant with structure of methane Allows for the formation of more bonds (4 unpaired e- s rather than 2)
Remember Steric # = 4 = tetrahedral arangement of those electron pairs = sp 3 hybridization
Four electron pairs tetrahedral arrangement of electron pairs N : : C : S
NH 3 : N 2 sp 3
sp Hybridization
Beryllium chloride Cl-Be-Cl Promote an electron from the 2s to the 2p orbital 2p 2p 2s 2s
Beryllium chloride ( BeCl 2 ) Mix together (hybridize) the 2s orbital and one 2p orbitals 2p 2s
Beryllium chloride ( BeCl 2 ) Mix together (hybridize) the 2s orbital and one 2p orbitals 2p 2sp (sphybridization)
The Be Cl! Bond in BeCl p Cl Be sp Be Cl Cl Be
The Be Cl! Bond in BeCl p Cl Be sp Cl Be Cl
sp 2 Hybridization
F Boron trifloride F Promote an electron from the 2s to the 2p orbital B F 2p 2p 2s 2s
Boron trifloride Mix together (hybridize) the 2s orbital and two 2p orbitals 2p 2s
(sp2_hybridization) Boron trifloride Mix together (hybridize) the 2s orbital and two 2p orbitals 2p 2 sp 2
B Boron trifloride
F F B Boron trifloride F
What about expanded octets? SF 6 PF 5
Hybridization of s, p, and d Orbitals Beginning with the third period of the periodic table 1 (3s orbital) + 3 (3p orbitals) + 1 (3d orbital) gives dsp 3 Permits 5 electron pairs (SN=5 trigonal bipyramidal ) 1 (3s orbital) + 3 (3p orbitals) + 2 (3d orbitals) gives d 2 sp 3 Permits 6 electron pairs (SN=6 octahedral )
p -Bonds
Review :Valence bond model Electron pair can be shared when the half-filled orbital of one atom overlaps with half-filled orbital of another.! Bond: orbitals overlap straight on, along the internuclear axis p Bond: side by side overlap of orbitals
Lewis model : Ethylene H p Bond H C C H H! Bond he carbon-carbon double bond of ethylene is a combination of a! Bond p Bond and Must have 1 sigma and 0 or more pi bonds between atoms. What s the hybridization of a C here?
Hybridization of C in C2H4 H H C C H Must have 1 sigma and 0 or more pi bonds between atoms. H # sigma bonds to C: 3 # lone pairs on C: 0 # hybrid orbitals needed on C: 3 + 0 = 3 Therefore, hybridization of C: sp 2 # singly occupied p orbitals (the leftovers ): 1 Therefore, # pi bonds to C: 1
Structure of Ethylene C 2 H 4 CH 2 CH 2 planar Bond angle 120 Requires hybridization different from sp 3
s "Bonding in Ethylene 2 sp 2
Orbital Hybridization Promote an electron from the 2s to the 2p orbital 2p 2p 2s 2s
Orbital Hybridization Mix together (hybridize) the 2s orbital and the two 2p orbitals 2p 2s
Orbital Hybridization Mix together (hybridize) the 2s orbital and the two 2p orbitals 2p 2 sp 2
p "Bonding in Ethylene 2p sp 2
p "Bonding in Ethylene
p "Bonding in Ethylene
Hybridization Example : : : Lewis Structure: O C O # sigma bonds to C: 2 # lone pairs on C: 0 # hybrid orbitals needed on C: Therefore, hybridization of C: 2 + 0 = 2 sp : # singly occupied p orbitals (the leftovers ): 2 Therefore, # pi bonds to C: 2 What about the hybridization of O? sp2
N2 sp hybridization plus 2 p leftovers sigma bond 2 pi bonds all bonds N N
Molecular Orbital Theory
(pibond) O O O N O O N O O N O O
(Magneticpropertiesofliquid)