Question

What is a sigma bond example?

Answer 1

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):

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`s + s`

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

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`s + p_z`

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

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`s + d_(z^2)`

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

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

(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)`)

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`p_z + p_z`

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

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`d_(z^2) + d_(z^2)`

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