Neutrons are Not Like Planets
Michael James Scharen
October 13, 2021

We have lived for many decades with the logo of the atom and electrons circling the nucleus.

I actually find it pretty annoying that the icon of a nucleus with electrons zinging around it in circles or ellipses like planets around a star is so ingrained with the public. Electrons occupy orbitals — but again, they are nothing like orbits around planets. The orbitals of electrons are different depending on their energy levels and those orbital levels have different numbers of electrons occupying them. This is a bizarre concept (and fun) if you’ve never looked at it before. An electron orbital is actually a probability cloud — another bizarre concept. For increasing energy levels of the electron, there is a hierarchy of orbitals. The lowest, or ground state is called the 1s orbital or a probability distribution which is spherical in shape. Getting back to the probability cloud and its meaning it is this. The s orbital is a spherical shell distribution of probability, for the 1s state which may be occupied by up to 2 electrons. What this means is there is a smeared out spherical shell about the nucleus where up to two electrons are most likely to be found. The Pauli Exclusion Principle says that no two electrons may occupy the same state, i.e. 2 in the 1s, 2 in the 2s, and 2 in each of the three p orbitals. These pairs are not in the same state though they are in the same orbital. One has an up spin and one a down spin. That’s a detail too deep for this explanation. To be brief, the1s shell or any of the 3 p shells may have an up spin electron and a down spin electron but trying to add another up or down spin to that orbital cannot be done snc there would be two like electrons in the same energy state/same orbital. Enough said. The farther in toward the nucleus or farther away from it, the probability of finding an electron there drops off rapidly.

Fig.1 - Diagram above showing the various types of electron orbital. From the top we have s, p, d, and f.

The probability cloud concept goes to the Heisenberg Uncertainty Principle which states that we can never really know the position of the electron precisely in combination with its energy or momentum at the same time. The next energy level, or level 2 has two regions where electrons might be found — a 2s or spherical region again plus three double-teardrop shaped p orbitals with the pointed end of the drop toward the nucleus. They are on each of the three spatial axes, x, y, and z. I’ve included a diagram of these sets here. They go on up to 3, 4, 5 etc. and are getting physically farther away from the nucleus with higher numbers, or higher energy levels and with differently shaped distributions. When an electron is given enough energy, it may jump from one orbital to one for a higher energy or be stripped away from the atom entirely. This creates a positively charged ion when the number of electrons is lower than the number of protons. Remember that the electrons are attracted to the nucleus because the protons are (+) and the electrons are (-) charges. Quantum mechanics explains why the electrons do not crash into the positively charged nucleus. The orbitals on this first diagram are color coded by each energy level. So the 2s level may have two electrons. Each of the 3 p orbitals may have two electrons. So the second level may have up to 8 electrons in all. Getting back to the distribution, the orbitals are all superimposed on each other centered on the nucleus. Another diagram shows the first and second levels together. The first level has only the spherical shell. The second level has a spherical shell plus the three double-teardrop shaped orbitals in the three axes.

Fig.1 - Diagram above showing the combination of two of the first orbitals. The structure gets complex very quickly.

This might be a bit much for this explanation for how electrons do not orbit like planets, but as one can see, the spatial distribution gets very complicated very quickly with all of the differently shaped electron clouds buzzing around the nucleus. One can see they look nothing like planetary paths. They are fuzzy and the states of the electrons are unknown until they make that quantum leap from one state to the other by releasing or absorbing a photon of energy at the specific wavelength to precisely cover that difference. This is what we mean by quantized, or quantum. The jumps are discrete. There is no in between, though there are a lot of finer levels not covered here. The last graphic shows fully up to level 4 and how many electrons are in the various orbitals for each of those levels. We only covered orbitals s and p, but there are also d and f as seen in the first diagram — all jumbled together. I hope this was a decent (and accurate) explanation of why and how electrons do not orbit like planets.

Fig.1 - Diagram above showing the progressively higher energy levels but with only two electrons maximum in each one. The structure gets complex very quickly.