[/caption]The electron cloud model is an atom model wherein electrons are no longer depicted as particles moving around the nucleus in a fixed orbit. Instead, as a quantum mechanically-influenced model, we shouldn’t know exactly where they are, and hence describe their probable location around the nucleus only as an arbitrary ‘cloud’.
It may surprise you but yes, typical science logos that show atoms with clearly defined electron orbits are now considered obsolete. It has been found that, contrary to Rutherford’s popular model, we can only describe electron locations in terms of most probable regions with fuzzy boundaries – thus the term ‘cloud’.
As mentioned earlier, the electron cloud model is a product of quantum mechanics. Among the basic concepts of this subject is its non-deterministic nature. Unlike Newtonian mechanics, which can predict with utmost accuracy the momentum and position of a particle once the forces, initial position, and momentum are known, quantum mechanics is devoid of that luxury.
In quantum mechanics, regardless of what the observer knows initially about a particle, he can only predict its succeeding location or momentum in terms of probabilities. At no given time will he be able to ascertain either one (location or velocity). In fact, according to the uncertainty principle, the more you know about the momentum of a particle, the less you know about its location and vice versa.
One typical example in quantum mechanics has an electron trapped in a box. Its location inside can only be determined in terms of probabilities represented by standing waves. Where there are crests, the likelihood of finding the electron there is highest, and where there are troughs, the likelihood of finding it there is lowest.
Note that the standing waves do not, in any way, represent where the electron should be found but only how high the probability of finding it there is compared to other locations in the box.
Now if we try to build on that oversimplified model and apply it to a 3-dimensional atom, the same principle will hold. Hence, when we see barbell-shaped and flower-shaped atoms (as in the thumbnail image above), the branching out regions are the ones where you will most likely find the electrons. These regions are known as electron orbitals
Note that the orbitals mentioned in the previous paragraph are formed by a hydrogen atom, i.e., by just one electron! Once when you have atoms with more electrons, the regions would spread out evenly into a spherical fuzzy ball, and is where the term ‘electron cloud’ is most appropriate.
We have some articles in Universe Today that are related to the electron cloud model. Here are two of them:
Some more from Physics World:
Tired eyes? Let your ears help you learn for a change. Here are some episodes from Astronomy Cast that just might suit your taste: