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Orbital Theory handout

Orbital Theory handout - PI MO or bond from sideways...

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Chemistry 140A (Prof. C. L. Perrin) ORBITAL THEORY ORBITAL = one-electron wave function ! (x,y,z) probability P ( x , y , z ) = [ ! ( x , y , z )] 2 Display orbital by drawing surface such that probability is 90% that electron is within surface. NODE = region of space where ! ( x , y , z ) = 0 and where P ( x , y , z ) = 0 ( ! changes sign across a node) MOLECULAR ORBITAL = LINEAR COMBINATION ("sum") of ATOMIC ORBITALS (for H 2 ) ! MO = c A ! 1sA + c B ! 1sB P ( x , y , z ) = ! MO 2 = c A 2 ! 1sA 2 + 2 c A c B ! 1sA ! 1sB + c B 2 ! 1sB 2 , increased in OVERLAP REGION Bonding molecular orbital allows electrons to be in internuclear region, attracted to both nuclei. Each molecular orbital can contain two electrons. ANTIBONDING ! MO' = c A ' ! 1sA - c B ' ! 1sB , has node in internuclear region, where electrons are excluded, thus of higher energy and usually empty, so ignored. SIGMA ( " ) MO or bond, from end-on overlap, preserves cylindrical symmetry.
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Unformatted text preview: PI ( # ) MO or bond, from sideways overlap, preserves nodal plane, used in multiple bonds. HYBRID ORBITAL = linear combination of s and p atomic orbitals on same atom ! hybrid = c s ! s + c p ! p (+ c p ' ! p' + …) In a hybrid orbital P ( x , y , z ) is increased on one side and reduced on other, so gives better overlap than s or p alone, where half the atom's electron density is "wasted". (bonding MO) ! MO = c A ! hybrid on A + c B ! hybrid on B Conservation of orbitals: number of hybrids = number of s and p orbitals used 2 sp hybrids from one s and one p 3 sp 2 hybrids from one s and two p 4 sp 3 hybrids from one s and three p Hybridization = sp 3-N # = sp 3-N double-2 N triple...
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