# Should chemistry students worry about quarks and such? [closed]

Even chemistry textbooks less than five years old start by describing atomic structure based only on protons, neutrons and electrons. Is an understanding of chemistry fundamentals likely to become out of date when the textbooks start to include quarks, leptons and the dozens of other sub-atomic particles?

• Why would they start to do it? – Mithoron May 12 '15 at 23:06
• There are only two types of fundamental particles in chemistry: electrons and nuclei. – Ben Norris May 13 '15 at 1:03
• There actually have been studies of chemistry based on particles other than electrons, protons and neutrons, especially using muons (which are leptons, not quarks). However, as the name "exotic atom" evokes, it's some very particular stuff. – Nicolau Saker Neto May 13 '15 at 1:13
• Well in my humble opinion a true scientist always pursues to expand their knowledge about the inner workings of nature. Therefore, if you like science you should attempt to at least understand something of everything. – AlanZ2223 May 13 '15 at 22:59
• Muons are pretty important in solid state chemistry; look up spin polarized muon spectroscopy... – J. LS May 14 '15 at 15:35

Is an understanding of chemistry fundamentals likely to become out of date when the textbooks start to include quarks, leptons and the dozens of other sub-atomic particles?

Well, the general chemisty books do already include leptons, at least electrons and usually positrons.

Other than protons, neutrons, electrons and positrons (and photons), I think that when discussing beta decay and electron capture, neutrinos and antineutrinos should be included, otherwise the nuclear reactions aren't really balanced (lepton number must be conserved). Alternatively, the general chemistry books could omit all discussion of nuclear reactions, as being physics.

Other than that, I think the rest of the particles can wait for physics class, rather than general chemistry class.

Beyond general chemistry, other particles are sometimes discussed in more advanced chemistry books, such as quantum chemistry texts, where examples involving muons are common.

For some chemistry topics, such as isotope differences in rotational-vibrational spectra of small molecules distinction between fermions and bosons is critical. Trying to explain the difference between fermions and bosons (and Fermi-Dirac statisitics vs Bose-Einstein statistics vs Boltzmann statistics) naturally leads to discussion of the standard model and the particles in the standard model. So by the time a student gets to physical chemistry, around the third year of college, they should have some understanding of the standard model.

Chemistry is governed by what electrons do, and generally... what valence electrons do. There really is no need to dive into subatomic particles. It may help explain what keeps a nucleus held together but we generally gloss over that aspect and simply have students accept this as a fact. Subatomic particles, of which there are many, are generally covered in physics. We usually touch upon them in nuclear chemistry when decay processes are introduced.

The main point here is that Chemistry is essentially all about what the electrons are doing.

I mean to be honest with you, when I was in Chem 1, we never went into the details of quarks and other sub-atomic particles except once; in nuclear chemistry. Even then, you didn't have to have an idea of these subatomic particles to understand what was going on.

So, if you think about it, wouldn't they (teachers) have changed the curriculum to include, other, dozens of subatomic particles if it was needed?

Although, you still have a good point. But, overall, from my definition of a chemistry student, I wouldn't think that worrying about quarks and other subatomic particles.

The real question is not ‘Why don’t books include X?’, but ‘What would change if books included X?’.

To the best of my knowledge and understanding, what protons, electrons and neutrons are is fundamental to understanding a wide range of stuff that happens in chemistry. (Yes, neutrons play a role for deuterium exchange effects etc.)

However, there is hardly anything that would change if descriptions included lower-level particles like quarks. I can’t think of any chemical reaction or other chemical process that cannot be sufficiently explained only going back to protons, neutrons and electrons — usually, even neutrons are irrelevant. So basically, you’re suggesting increasing complexity with no added benefit to the learner. Why would one do that? Just for the sake of correctness? If anything, a note that protons and neutrons are made up of smaller particles suffices for any beginner’s level textbook.

In fact, there is quite a lot of chemistry that can be just explained with the concepts of atoms and bonds. The only reason why the sub-atomic particles are included in the first place, is because salts are introduced early and can be explained a lot better, if electrons and nuclei are known. (And it eases the explanation of ‘what exactly is a bond?’)

I'm going to take a shot at this question from a different angle, aiming for a more objective analysis. For that, I wish to bring up several concepts. Bear with me!

First of all, what do we mean when asking if something is relevant or not to Chemistry? A precise and exact definition is not trivial, but let us consider a simple argument: chemical reactions are pretty important in Chemistry! In other words, we like to see atoms swapping around positions. It turns out that we have a fair idea of how quickly these events happen. We know that bonds in molecules vibrate at certain frequencies, which is how infrared spectroscopy works. The quickest bonds to vibrate do so at around $\rm{3500\ cm^{-1}}$, which implies a frequency of about $\rm{10^{14}\ Hz}$. This establishes a useful timescale - the fastest atomic displacements relevant to bonding in a molecule happen on the order of $\rm{10^{-14}\ s = 10\ fs}$. This means even the fastest chemical reactions need at least about this much of time to happen. Any event which begins and ceases within a timescale much shorter than $\rm{1\ fs}$ means that molecules don't even have time to react to the event. Even a molecule in a reaction transition state, as short-lived as it is, would be essentially frozen during time intervals much smaller than this. There are important processes which happen faster than $\rm{1\ fs}$, such as electronic transitions and nuclear decay, but they are important in Chemistry because what matters here is not how long the transition takes, but that the resulting state is sustained for around $\rm{1\ fs}$ or more before it decays. As an interesting aside, virtual electronic states used in Raman spectroscopy exist for times as long as $\rm{0.1\ fs}$, which further shows how this scale is too quick for molecules to respond.

Now for subatomic particles. Not counting antiparticles, there are at least 17 types of fundamental particles (though 4 of those are force carriers, and the Higgs boson is something else entirely, so we'll put those aside), and over a hundred composite subatomic particles. Yet, for some reason, almost all of Chemistry only deals with three fundamental matter particles (the electron, up quark and down quark), and two composite particles (protons and neutrons, i.e. the up-up-down and up-down-down triquarks, respectively). Why is that so?

Without getting into the nitty-gritty details of particle physics, it turns out that particles tend to decay into their lightest possible relatives while obeying certain rules, such as charge conservation. Electrons are the lightest negatively-charged particle, so they are indefinitely stable (the same is true for positrons, the lightest positively-charged particle). Protons could conceivably decay into something lighter thanks to the positron, but in this case there is another type of conservation law which strongly forbids them to do so (baryon number conservation), so if they are not indefinitely stable, they are at least very long-lived ($\rm{10^{35}}$ $\rm{a}$ or more).

Neutrons are an interesting case. They're very slightly heavier than protons, by about 1%. This is enough to allow for decay, and indeed a free neutron has a mean lifetime of about $\rm{15\ min}$ before it suffers $\beta^-$ decay into a proton. If this happened to every neutron, the Universe would be filled solely with hydrogen, and life could not exist. Remarkably, the mass difference between protons and neutrons is small enough that it can be compensated by the stabilising nuclear forces inside the nucleus, and thus neutrons inside nuclei are stable with respect to decay for an amount of time comparable to the proton.

So up to now, we know that electrons, protons and neutrons are three examples of subatomic particles which are so long-lived that we can expect them to be relevant in chemical timescales. Are there any more? This is where things go awry. The next most stable subatomic particle other than the ones I just cited is the muon, a particle identical to the electron except for its larger mass, with a mean lifetime of just $\rm{2.2\ \mu s}$. This is still many of orders of magnitude more than the femtosecond benchmark established earlier, and in fact muons can display meaning chemistry, even taking part in reactions [1], [2]. However, you can imagine that processes involving muons are expected to be much, much rarer, and not have as much importance in chemistry. This is not to say that muons are irrelevant to Chemistry, just that they are of interest only in a much narrower range of circumstances relative to electrons, neutrons and protons. The problem is even worse for other subatomic particles, which often have much shorter lifetimes. Looking at some lists of particles, such as baryons, mesons and leptons, one sees just how short-lived they are; about half of them decay far quicker than $\rm{1\ fs}$ and could not even in principle partake in chemistry. There are still a couple dozen of particles which decay between $\rm{100\ ns}$ and $\rm{1\ fs}$, for which chemistry could exist at an even more limited scope, but again these are rarely relevant.

After all the information exposed above, should the average Chemistry student worry about these subatomic details? No, I don't think so. In fact if these issues were to be mentioned as more than a passing comment in when first teaching the structure of matter, I believe it would be counter-productive. That said, I do think it's a shame that an enormous majority of chemists never seem to peer a little deeper into the structure of matter, even years after graduating. It would be nice if at least knowledge of the fundamental particles were more disseminated. The Standard Model of particle physics is quite an amazing achievement, and there's more than enough beauty to appreciate even without breaking out the massive integrals!