HF H: 1s1F: 1s22s22p5

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• HF H 1s1 F 1s22s22p5
• Overlap between the valence orbital of H (1s) and
  valence orbital of F (2p) to form a s bonds

Note electron spin is paired in the s orbital
By definition z is the direction along the
internuclear axis
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• N2 N 1s22s22p3

The two pz orbitals from each N can overlap to
form a s orbital. The px and py orbitals are
perpendicular to the internuclear axis
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s bond - overlap of two pz orbitals
p bond - overlap of two px orbitals and/or two py
orbitals
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In a p bond, electron density has a nodal plane
that contains the bond axis
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• According to the VB theory
• A single bond is a s-bond
• A double bond is s-bond plus a p-bond
• A triple bond is a s-bond and two p-bonds.
• VB theory assumes bonds form
• when unpaired electrons in valence shell atomic
  orbitals pair
• the atomic orbitals overlap end to end to form
  s-bonds or side by side to form p-bonds.

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Hybridization of Orbitals

• C Is2 2s2 2p2

VB theory, as described so far, would predict
that C can form just two bonds
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• In CH4, C forms four bonds.
• C needs four unpaired electrons so that each can
  pair with a H atom - need to revise valence-bond
  theory
• Promote a 2s electron to a 2p orbital - this
  requires energy.
• But now C has four unpaired electron and since
  bonding releases energy the cost of promoting is
  overcome by the lowering of energy on bond
  formation

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• CH4
• Promoting a 2s electron to 2p allows C to have
  four unpaired electrons.

All bonds on CH4 are equivalent Mix the 2s and
the three 2p orbitals to form four hybrid
orbitals all of the same energy and spatial
distribution - hybridization. One s three p
four sp3 orbitals
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• Hybrid orbitals are constructed on an atom to
  reproduce the electron arrangement of the
  experimentally determined shape of the molecule.
• In CH4 each sp3 orbital has one unpaired
  electron
• Each overlaps with a 1s orbital of H to form
  s-bond
• The four resulting s-bonds point towards the
  corners of a tetrahedron.
• All four s-bonds are identical

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• Ethane C2H6
• Each C has four sp3 hybrid orbitals, pointing
  towards the corner of a tetrahedron, each with
  one electron
• Three of these four overlap with three H atoms
  forming s-bonds (C sp3, H 1s).
• The C-C bond is formed by an overlap of the
  remaining sp3 orbital on each C forming a s-bond
  (C sp3, C sp3).

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• NH3
• H Is1 N Is2 2s2 2p3
• Hybridize the 2s and 2p orbitals in N to form
  four sp3 hybrid orbitals.
• One of the sp3 has two paired electrons - the
  lone pair on N
• The three other sp3 orbitals form s-orbitals with
  each of the three H 1s orbitals

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• H2O
• H Is1 O Is2 2s2 2p4
• Hybridize the 2s and 2p orbitals in O to form
  four sp3 hybrid orbitals.
• O ?? ? ?
• ?? 2p
• 2s
• O ?? ?? ? ?
• sp3
• Two of the sp3 have two paired electrons - the
  two lone pairs
• The two other sp3 orbitals overlap with H 1s
  orbitals

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An s orbital and two p orbitals can hybridize to
form three sp2 hybrid orbitals which point to the
corners of an equilateral triangle - trigonal
planar geometry Example BF3
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• An s and a p orbital can hybridize into two sp
  orbitals that point in opposite directions -
  linear geometry

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• PCl5 P Ne 3s2 3p3 Cl Ne 3s2
  3p5
• P ? ? ? Cl ?? ?? ?
• 3p 3p
• ?? ??
• 3s 3s
• Promote a 3s electron to the 3d orbital
• P ? ? ? ? ? _ _ _ _
• sp3d empty 3d

Valence shell expansion - expansion to include d
orbitals along with s and p orbitals
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One 2, three p, and one d orbital form five sp3d
hybrid orbitals, each pointing towards a corner
of a trigonal bipyramid
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• One 2, three p, and two d orbital form six sp3d2
  hybrid orbitals, each pointing towards a corner
  of a octahedron

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SF6 S Ne 3s2 3p4 F He 2s2 2p5 S
?? ? ? 3p ?? 3s Include two 3d
orbital and hybridize one s, three p and two
d S ? ? ? ? ? ? _ _ _ sp3d2
empty 3d
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Multiple Bonds

• Ethylene CH2CH2
• Experimental data all six atoms lie in the same
  plane and the H-C-H and C-C-H bond angles are
  120o.
• Trigonal planar geometry indicates that each C is
  sp2 hybridized

For each C two of the sp2 orbitals bond with two
H 1s orbitals to form s-bonds, The third Csp2
bond on each bond with each other to form a C-C
s-bond
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• The pure 2p orbitals on each C overlap to form
  a p-bond between the two C atoms
• The electron density of this p-orbital lies above
  and below the axis of the C-C s-bond

http//www.whfreeman.com/chemicalprinciples/
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• Acetylene C2H2
• Linear molecule each C is sp hybridized, leaving
  two pure p orbitals on each C

http//www.whfreeman.com/chemicalprinciples/
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Multiple bonds are formed when an atom forms a
s-bond by using an sp or sp2 hybrid orbital and
one or more p-bonds by using un-hybridized p
orbitals
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• Formic acid HCOOH

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