The universe is an Atom

Electron cloud is a term used, if not originally coined, by the Nobel Prize laureate and acclaimed educator Richard Feynman in The Feynman Lectures on Physics for discussing "exactly what is an electron?". This intuitive model provides a simplified way of visualizing an electron as a solution of the Schrödinger equation. In the electron cloud analogy, the probability density of an electron, or wavefunction, is described as a small cloud moving around the atomic or molecular nucleus, with the opacity of the cloud proportional to the probability density.

The electron cloud formulation better describes many observed phenomena, including the double slit experiment, the periodic table and chemical bonding, and atomic interactions with light. Although lacking in certain details, the intuitive model roughly predicts the experimentally observed wave-particle duality....

In the electron cloud model, rather than following fixed orbits, electrons bound to an atom are observed more frequently in certain areas around the nucleus called orbitals. The electron cloud can transition between electron orbital states, and each state has a characteristic shape and energy, all predicted by the Schrödinger equation, which has infinitely many solutions. Experimental results motivated this conceptual refinement of the Bohr model.

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There are different models of the structure of the atom. One of the first models was created by Niels Bohr, a Danish physicist. He proposed a model in which electrons circle the nucleus in "orbits" around the nucleus, much in the same way as planets orbit the sun. Each orbit represents an energy level which can be determined using equations generated by Planck and others discussed in more detail below. The Bohr model was later proven to be incorrect.

The "accepted" model is the quantum model. In the quantum model, we state that the electron cannot be found precisely, but we can predict the probability, or likelihood, of an electron being at some location in the atom.

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Chemists care about where electrons are in an atom or a molecule. In the early models, we believed that electrons move like billiard balls, and followed the rules of classical physics. The graphic below attempts to show that earlier models thought that we could identify the exact path, position, velocity, etc. of an electron or electrons in an atom:

image source: http://www.shodor.org/unchem/basic/atom/classpath.gif


A more accurate picture is that the electron(s) reside in a "cloud" that surrounds the nucleus of the atom. This concept is shown in the graphic below:

image source: http://www.shodor.org/unchem/basic/atom/quantum.gif


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