Electron cloud

Electron cloud is a term used for introducing the concept of wavefunction in low-level pedagogical introductions to atomic physics, molecular physics, chemistry or quantum chemistry. This idea corresponds to delocated electrons moving or standing like clouds around the atomic or molecular nuclei. This is indeed a better image than the very common image provided by the Bohr model which commonly leads to a visualisation of electrons driving around the nuclei along orbits like the planets around the sun.

This representation is related to the idea that the electrons are not precisely located around the atomic or molecular nuclei but must instead be described by probability amplitudes or wavefunctions which provides the probability to find electrons in a given region of space (for example along a particular chemical bond). These mathematical functions of the coordinates of all electrons are often expressed in terms of electronic configurations or Slater determinants which are in turn expressed in terms of atomic or molecular orbitals. One can represent the theory also in terms of the electron density which is a function of one electron only. This approach is called the density functional theory. Both the molecular orbital and density functional approaches are the basic elements of modern quantum chemistry and of computational chemistry.