14 3.4 Electron cloud and orbital
- The electron cloud expresses the region of space around the nucleus in which the electron is likely to be found, in all directions and dimensions. It is denser where the probability is higher.
- Within the cloud there are regions where the probability of finding the electron is greatest; each such region is called an orbital.
- The mathematical solution of Schrödinger's equation gives four numbers, the quantum numbers, that describe each electron in a multi-electron atom.
✍️ Worked examples
Worked example 3.1.
- Why is the picture of "an electron running on a circle like a planet" no longer accepted?
- Because we cannot know the exact position and speed together (Heisenberg); we can only give a probability map, the orbital.
- Orbits (fixed paths) were replaced by orbitals (regions of probability).
Worked example 3.2.
- Compare "orbit" and "orbital".
- An orbit (Bohr) is a definite circular path at a fixed distance, in a plane.
- An orbital (wave mechanics) is a three-dimensional region around the nucleus where the electron is most likely to be found, with a characteristic shape.
Worked example 3.3. Match each scientist to the idea: Thomson — positive sphere with embedded electrons; Rutherford — nucleus; Bohr — quantised energy levels; Heisenberg — uncertainty principle; Schrödinger — wave equation and orbitals.