Particle Physics, Physics

But What Makes Up The Atom?

Last time, we found out that an atom is made up of protons, neutrons and electrons, but that’s just the beginning. Welcome to the world of particle physics and subatomic particles!

If you missed my previous post, I recommend reading that first! You can also read an updated version that includes the problems with the standard model here!

Protons and Neutrons, are a type of composite particle called a hadron, meaning that they are made of quarks. Quarks are a type of Sub-atomic particle described by the Standard Model. This means that, as far as we know, they can’t be split down any further (there has been some speculation on this, giving rise to interesting concepts like string theory).

EDIT (26/4/21): However, recently more and more evidence has been piling up to suggest that perhaps the standard model isn’t such a perfect description of the world around us! Read the updated blog post here


The Standard Model (see  image caption)
The Standard Model, showing the three generations of Quarks (purple) and Leptons (green) on the left (lightest/most stable generation far left) and different bosons (red and yellow) on the right

As you can see from the picture, quarks are matter particles, called fermions. The quarks that are the constituents of atoms are up and down quarks. These are the first generation of quarks, meaning that they are the lightest and by far most stable. The other two generations are unstable, so the composite matter they do create decays (turns into simpler forms or entirely different particles) quickly. They are only found in very high energy environments and collisions, such as cosmic rays or particle accelerators.

two diagrams: proton and neutron
proton: large circle with three smaller circles within it, all different colours (red, green, blue). Two are labelled up and one is labelled down (quarks)
neutron: same as proton diagram except two are labelled down and one is labelled up.
Diagram of a Proton and a Neutron, showing the different components and ‘colours’.

A Proton is made of 2 up quarks and a down quark. Up quarks have a charge of +⅔, and down quarks have a charge of -1/3 , so the charge is +1 (positive), which we know already!

Neutrons, on the other hand, are made from one up quark and two down, creating an overall neutral charge.


The other type of Fermion is the Lepton, which includes generations of electron and neutrino. That’s right, electrons are elementary particles in their own right, unlike protons and neutrons. It’s why they move within fuzzy orbitals, not nice predictable orbits, because fundamental particles obey laws of quantum mechanics, like the Heisenberg Uncertainty Principle. Like quarks, the most stable generation is the first one, hence it is electrons in atoms, not muons or taus (by the way , tau is pronounced t-OW, like the sound you make when you stub your toe). Electrons have a charge of -1, therefore an electron+proton+neutron= neutral!

Neutrinos are the other type of Lepton, and carry no charge and have an incredibly tiny mass, far less than that of the electron! It has even been hypothesised to have no mass at all! Due to this, they are incredibly difficult to detect, despite being relatively abundant, as they come from atomic decay and fusion in stars! Just to put their abundance into context, about 65 billion of them pass through one square centimetre (about the size of your thumbnail) every second! That means that there are about 100 trillion passing through your whole body at once, completely undetected!


Electrons stay moving around the nucleus because of the electrostatic attraction formed from the difference in charges: opposites attract.

But how does the nucleus stay together?

It’s all down to a fundamental force called the Strong Force (which is carried by a particle called the Gluon, which is a type of Boson). This is, as the name suggests, the strongest force (welcome to another episode of particle physicists are really creative), and unlike other forces, it actually increases with distance, similar to how it gets harder to pull on a spring, the further you pull it. It is for this reason that quarks cannot be free, they are always found ‘glued’ to other quarks in hadrons or mesons. This is actually what makes Quarks and Leptons different from each other: Quarks interact with all 4 fundamental forces, whereas Leptons interact with all but the Strong Force. This is also why electrons can become delocalised, for example in metallic bonding in metals, allowing an electric current to pass through!


To Summarise, atoms aren’t just made of protons, neutrons, and electrons, but of more fundamental particles: Quarks, Electron and Gluons (Boson of the Strong Force)! If you have any questions or comments, make sure to leave them in the comment section below and I’ll try to answer them!


If you can’t trust an atom… trust in science!

☆it’s like magic, but it’s true whether you believe in it or not!☆

See you next time!


Stay Curious! And remember, never trust an atom! On cosmic web background

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