What is a sigma bond example?

1 Answer
Truong-Son N.
Apr 13, 2016

If we follow the convention that:

  • The internuclear axis of a linear molecule is the #z# axis
  • The internuclear axis of a nonlinear molecule is the #y# axis

...then any two orbitals overlapping head-on is a #\mathbf(sigma)# molecular orbital.

Thus, noting that there are other possibilities, the following orbital combination examples would work (excluding #f# orbitals, which are quite complex and hard to describe):

#s + s#

Inorganic Chemistry, Miessler et al., pg. 118

EX: #"H"-"H"# bond in #"H"_2#

#s + p_z#

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EX: #"H"-"Cl"# bond in #"HCl"#

#s + d_(z^2)#

Inorganic Chemistry, Miessler et al., pg. 121

EX: #"Zn"-"H"# bond in #"ZnH"_2#

#p_y + d_(z^2)# (axial, nonlinear) --- left
#p_y + d_(x^2-y^2)# (equatorial, nonlinear) --- right

Inorganic Chemistry, Miessler et al., pg. 365

(yes, these are #p_y# molecular orbitals aligned along #z# and #x# axes. That's right.)

EX:

  • #"NH"_3#'s #"N"-"Cr"# bond in #["Cr"("NH"_3)_2("NCS")_4]^(-)# (#p_y + d_(z^2)#)
  • #"NCS"#'s #"N"-"Cr"# bond in #["Cr"("NH"_3)_2("NCS")_4]^(-)# (#p_y + d_(x^2 - y^2)#)

#p_z + p_z#

Inorganic Chemistry, Miessler et al., pg. 120

EX: #"Cl"-"Cl"# bond in #"Cl"_2#

#d_(z^2) + d_(z^2)#

Inorganic Chemistry, Miessler et al., pg. 122

EX: #"Mn"-"Mn"# bond in #"Mn"_2("CO")_10#

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