Most people have a picture of the electron as a point-like particle. That infinitesimal point is the source of a negative electric field, and therefore if two electrons are brought close together they will repulse each other. Right? Well…the answer is that sometimes they do, and sometimes they don’t. In this post I want to provide some examples of when electrons are NOT repulsive. Of course if electrons actually were point-like particles they would always be repulsive but the “point-like” model is an over-simplification.
Notice that I’m not proposing anything that contradicts current science. I am just trying to point out that some of our mental models, and even things you may find written in text books, is not quite the whole story.
Consider the Hydrogen atom, the simplest and most abundant atom in the Universe. The most common isotope of Hydrogen has a single Proton and a single Electron. In its lowest energy state the electron forms a spherical shell surrounding the Nucleus. In that low-energy state the electron shell has no orbital angular momentum (I.E. it is stationary). Essentially it is symmetrical “cloud”. Now consider a Helium atom. The nucleus now has two Protons and two Neutrons. In an Electrical neutral state it has two electrons. These electrons form a spherical shell as before where they have opposite spin. Once again, in the lowest energy state, there is no orbital angular momentum, and now even the electron spins cancel, removing the spin angular momentum as well. If you compare the Helium atom to the Hydrogen atom it is smaller. In fact, Helium is the smallest of all atoms.
But how can that be? The two electrons in Helium are taking up less volume than just one electron in a Hydrogen atom. Don’t the two electrons repel each other? Apparently not.
In that example we see no evidence of repulsion. Now consider a case where two electrons actually provide an attractive force. If you suppose that we begin with a gas made up of Hydrogen atoms they will fuse together in pairs, releasing energy as they do so. The end result is Hydrogen molecules. Each molecule contains two Protons. The Protons are held together in spite of the mutually repulsive force between them. Outside the pair of protons is an ellipsoid shaped cloud of two electrons.
This seems rather strange: the attractive force between the two electrons is not only sufficient to overcome the repulsive force between the two protons, it even provides for an energy surplus after the merger.
In 1928 Paul Dirac found a way to combine Special Relativity and the Quantum Wave function such that it not only explained the odd behavior of the electron (E.G. its spin), it also predicted a new particle — the positron. The positron was confirmed just a few years later. So for almost 95 years we have had an explanation for situations where electrons can be attractive. However this deeper explanation rules out over-simplified pictures that still show up in popular explanations, and even text books.
I plan to do another post on this topic showing an analysis of a case where a macro (human) scale electrostatic charge appears to be repulsive, but actually involves attraction, not repulsion. Stay tuned.
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