V-B theory can’t explain some observations about Hybridized Orbitals V-B theory can’t explain some observations about molecular compounds without the concept of hybridized orbitals. i.e., covalent (NM/NM) compounds

…the central atom SHOULD be… …but is ACTUALLY hybridized to be… …the result then being… In… (LS) BeF2 2 hyb. sp orbs. 2 unhyb. 2p orbs. : Be F 2s 2p sp 2p B : F BF3 3 hyb. sp2 orbs. 1 unhyb. 2p orb. 2s 2p sp2 2p C H CH4 4 hyb. sp3 orbs. 2s 2p sp3 H2O O H : 4 hyb. sp3 orbs. 2s 2p sp3 P : F PF5 5 hyb. sp3d orbs. 4 unhyb. 3d orbs. 3s 3p 3d sp3d 3d XeF2 5 hyb. sp3d orbs. 4 unhyb. 5d orbs. : Xe F 5s 5p 5d sp3d 5d : Xe F 6 hyb. sp3d2 orbs. 3 unhyb. 5d orbs. XeF4 5s 5p 5d sp3d2 5d

KEY: EDG  hybridization of central atom linear  sp trig. planar  sp2 tetrahedral  sp3 trig. bipyr.  sp3d octahedral  sp3d2

sp hybridization sp hybridization occurs when one s and one of the three p orbitals hybridize. It results in the creation of two sp hybrid orbitals (orange). The other two p orbitals (purple) are unhybridized; they retain the “figure-8” or “dumbbell” shape.

.. Multiple Bonds s (sigma) bonds are bonds in which the e– density is along the internuclear axis. N H .. The bonds in ammonia are s bonds. -- These are the single bonds we have considered up to this point. -- e.g., s-s, s-p, or p-p overlap, and also p-sp hybrid overlap sigma (s) = single Multiple bonds result from the overlap of two p orbitals (one from each atom) that are oriented perpendicularly to the internuclear axis. These are p (pi) bonds. pi, multiple, unhybridized

For each carbon atom, there p bonds are generally weaker than s bonds because p bonds have less overlap. For ethene (C2H4)… C=C – H C H For each carbon atom, there are 3 sp2 hybridized orbitals; these form s bonds (- - - -) with C or H. Where unhybridized orbitals overlap, a p bond ( ) is formed.

Single bonds are s bonds. e.g., C2H6 Double bonds consist of one s and one p. e.g., C2H4 Triple bonds consist of one s and two p. e.g., C2H2

Experiments indicate that all of C2H4’s atoms lie in the same plane. This suggests that p bonds introduce rigidity (i.e., a reluctance to rotate) into molecules. -- p bonding does NOT occur with sp3 hybridization, only sp and sp2 -- p bonding is more prevalent with small molecules (e.g., C, N, O) (Big atoms don’t allow enough p-orb. overlap for p bonds to form.)

[ ] .. Delocalized p Bonding Localized p bonds are between… two atoms only. [ ] N =O O– .. O – -- e.g., C2H2, C2H4, N2 Delocalized p bonds are “smeared out” and shared among… > two atoms. -- These are common for molecules with… resonance structures. The nitrate ion (NO3–) has delocalized electrons. -- The electrons involved in these bonds are delocalized electrons.

C H Consider benzene, C6H6. -- Each carbon atom is ___ hybridized. sp2 -- This leaves... a 2p orbital on each C that is oriented to plane of m’cule. -- 6 e– shared equally by 6 C atoms

[ ] .. .. .. Which of the following exhibit delocalized bonding? 24 e– H–C–C–C–H O = .. – H3C–C–CH3 O = “NOPE.” propanone O–S=O .. SO2 18 e– “YEP.” sulfur dioxide (res.) [ ] S –O O– .. O 2– SO42– 32 e– “NOPE.” sulfate ion