Name of particle Relative charge Relative mass Proton +1 1 Electron -1 1/1840 Neutron 0 1

Annotation: The following information may also be noted for each of the fundamental sub-atomic particles, of which a typical atom consists.

Let’s engage in a simple, if not basic, study of the above table.

Firstly, in that the proton, neutron and electron are three fundamental subatomic particles, there are also other basic subatomic particles. An example of other known particles include alpha and beta particles. But bracketing the existence of these other particles for a moment, what is interesting about the humble proton, neutron and electron is how they interact with one another.

Although the Bohr model is outdated, replaced with the more accurate model of an electron cloud (diagram below, courtesy of Berry Perry), the former offers a more intuitive model directly relatable with human experience. This is one reason why it is still taught in undergraduate courses. When people thinking of electron orbitals, they seem to often imagine examples in the form of planetary orbits or something similar, and with that there is the idea – as when using the Bohr model – that we can accurately calculate the velocity of an orbiting electric and its position and so on. But this is not correct. In fact, the Bohr model is not correct. To explain why it is not correct, one might refer to the Heisenberg Uncertainty Principle. This is something I will write more about in a separate post, as there seems to be confusion in popular accounts between this principle and the observer effect (it is wrong to conflate the two). But the main idea I want to grab at here is that, just as the more intuitive Bohr model is not correct, science often teaches us there is a limit to the knowledge of human experience. This is why, in my estimation, a lot of people seem to struggle with understand quantum mechanics. It is not intuitive, and it generally does not corroborate with what one often observes in their daily experiential experience. So when it comes to things like an electron orbiting the nucleus of some atom, it is more accurate to think of a cloud as opposed to a neat classical orbital model. But if we take it one step further: in quantum theory, we learn that even the electron cloud is outdated, as the depiction of many points is not accurate insofar that the electron cloud is theorized to be more “smooth”.

Instead of the Newtonian, mechanical view of the configuration of electrons, which is modeled from a more classical orbital configuration, such as found in the Bohr model, electronic orbitals and sub-orbitals are much more complex. It is from within the quantum model of electron configuration that we understand how, instead of the electron being in a classically defined and fixed orbit around the nucleus (think of a planet around a star), the description is one of orbitals as probability density functions. In fact, in thinking of electrons, one can think of them as standing matter waves (or at least there is an analogy here) within the limit of a certain energy values. And this leads to understanding electron orbits as orbitals.

In this sense, an orbital, which is a wave function, helps account for any volume of space around the nucleus in which there is x probability of finding an electron. Additionally, and before moving on to the illustration, it is important to highlight that there are two primary features of the orbital: the energy shell, n, and the corresponding periods on the periodic table. But even the word “orbital” – much like the word “shell” or “energy shell” – can be susceptible to misinterpretation, wherein one may be inclined to resort to some classical mechanical definition. Electron orbitals aren’t so neatly defined as to be clean edged containers in which the electron absolutely resides and orbits.

What is useful about the illustration of the model of the electron cloud is how, if one were to take many snapshots of electrons, the image like the one above would form insofar that the probability density would be closer to the nucleus. The further out the less likely (a much lower probability) an electron might be found. But, again,  even the depiction of many points could easily represent the location of the electron, and this isn’t entirely accurate.

Having said that, and understanding that there are theoretical reasons as to why an electron can occupy space behind the probability density orbital, or electron shell, what the Bohr model highlights is how an atom can be divide into protons, neutrons and electrons. The proton, which is positively charged (+1 relative charge), is also a nucleon. In other words, if most of the mass of an atom is in the nucleus, this area – and I use the word “area” cautiously – is made up or constituted by protons and neutrons, which we can also call nucleons (Wang, ND).

Furthermore, neutrons have no relative charge – hence they are neutral. For this reason, they do not interact with protons and electrons (although along with protons they make up most of the mass of an atom). Additionally, the neutrality of the neutron is why an atom has a neutral charge. It also explains the existence of electron orbit, as this has to do, in simplistic terms, with the interaction between the positively charged proton and the negatively charged electron. The positively charged proton within the nucleus is important with respect to the fundamental relation of the atomic dynamic, because electrons, which are negatively-charged, interact outside the nucleus with the proton. That is to say there is a force of attraction due to the opposite charges, and this force enables the relative orbit of the electron around the positive nucleus.

If an atom is electrically neutral, this is due to how the charges of the positive proton and the negative electron are of equal magnitude. Thus, they balance or cancel out. Hence, the ratio that a neutral atom will have one electron for every proton.

Having said all that, in particle physics we learn that even protons and neutrons are “composite objects”, as physicists delve deeper into the nature of matter and into the study of such particles as quarks and leptons (among others). In my field of study, particle physics, there is an incredibly exciting frontier of science to potential be revealed as we move further into the 21st century. At CERN and elsewhere troves of data await analysis. The hunt for new particles continues, and there remains much to be accomplished in particle physics in the decades ahead. The Standard Model is an incredible achievement; but it’s also incomplete and the exciting possibility of a new physics stares back at us from the furthermost distant horizon.

In a future post I’ll expand on this simple discussion toward a more deepened and complex view.

References

Adams, S. and Allday, J. (2013). Advanced Physics. Oxford University Press. Oxford, UK.