Node
A region within an orbital where the probability of finding an electron falls to zero.
Formula / equation
total nodes = n − 1
Unit
Dimensionless
In depth
Radial nodes are spherical surfaces and number n − l − 1; angular nodes are planes or cones through the nucleus and number l. Nodes arise because orbitals are standing waves, and their count rises with energy, which is why higher orbitals are both larger and more structured.
Examples in the real world
The 2s orbital has one radial node; each 2p orbital has one angular nodal plane through the nucleus.