Question

Can bonding molecular orbitals have a node? If so, what does it look like?

Answer 1

Yes, bonding molecular orbitals can have nodes.

Explanation:

When two atomic orbitals overlap, they form two molecular orbitals, of which one is bonding and one is antibonding.

For example, two `p` orbitals overlap to form a `π` (bonding) and a `π`* (antibonding) orbital.

We can see this in ethene, buta-1,3-diene, and benzene.

Ethene

(from www.dlt.ncssm.edu)

Each time you go up an energy level, you get another node.

Buta-1,3-diene

If you use four atomic `p` orbitals to make the molecular orbitals in butadiene, you get four new `π` orbitals.

Each level up has one more node.

The four `p` electrons go into the two bonding orbitals, one of which has a node.

Benzene

The six `p` orbitals in benzene combine to form six `π` orbitals, of which three are bonding and three are antibonding.

(from jwhitesell.ucsd.edu)

The lowest-energy orbital, `π_1`, has zero nodes and has the familiar doughnut shape. It holds two `π` electrons.

`π_2` and `π_3` are degenerate bonding orbitals with one node. The node in `π_2` is at right angles to the node in `π_3`. Each orbital contains two electrons.

`π_4` and `π_5` are degenerate antibonding orbitals with two nodes at right angles to each other.

`π_6` is an antibonding orbital with three nodes.