Question

Describe the formation of single, double, and triple bonds by orbital overlap?

Answer 1

Single bonds are made when two orbitals overlap head-on (such as two `s` or two `2p_z` orbitals along the `z` axis) to make a sigma (`sigma`) bond. In other words, a single bond consists of one `sigma` bond.

Example:

• Let a `"H"-"H"` bond to be made be along the `z` axis.

`"H"_2` uses one `1s` orbital from each hydrogen to make a `"H"-"H"` bond through a `1s-1s` head-on orbital overlap. A head-on overlap must occur to make the only component of a single bond.

A double bond incorporates an additional `pi` bond, which is sidelong orbital overlap (such as a `2p_x` with a `2p_x` orbital). So, a double bond consists of one `sigma` and one `pi` bond.

Example:

• Let a `"C"="C"` bond to be made be along the `z` axis.

The `2p_z` orbital of each carbon overlaps head-on to make one `sigma` bond.

Then, the `2p_x` of each carbon overlaps sidelong to generate a `pi` bond. This gives us both components of the double bond.

A triple bond just incorporates one more `pi` bond than a double bond, so it consists of one `sigma` and two `pi` bonds.

Example:

• Let a `stackrel((-))( :"C")-=stackrel((+))("O": )` bond to be made be along the `z` axis.

As before, the `2p_z` orbital of each atom overlaps head-on to generate a `sigma` bond. This is always necessary as a first step.

Then, a `2p_x` orbital from each atom overlaps as before to generate one `pi` bond.

The `2p_y` orbital is finally incorporated from each atom to generate the second `pi` bond. That gives us all three components of a triple bond.