Chemistry · Chapter 8

Sigma and Pi: Two Ways to Overlap

Orbitals can meet end to end or side by side. Pick a pairing, then use the spin slider to twist atom B about the bond axis. Only one kind of overlap survives the twist.

The overlap top: side view · bottom: looking down the axis

SIDE VIEW LOOKING DOWN THE BOND AXIS

What you are seeing

Pick a pairing to begin.

Pick the pairing

σsigma bond holds

Live numbers

Twist angle0 degrees
Relative overlap100%
Density on the axishighest there
Nodal planenone through the nuclei
Free to spinyes
Typical carbon value347 kJ/mol
The rule behind it
Overlap follows the cosine
Head‑on overlap is round about the axis, so spinning it changes nothing. Side‑on overlap needs the two p orbitals parallel. Twist them and the shared space falls off as the cosine of the angle. At 90 degrees it reaches zero.