The standard model describes all of the known particles of matter and how they are affected by 3 particular forces (I will explain these 3 forces later). To start, I’m going to assume that I have to explain everything from scratch so sorry if you already know some of this. Almost everything we see around us consists of matter, and specifically atoms. Atoms are made up of 3 particles: electrons, protons and neutrons. Now, as you may know, electrons are attracted to the protons in the nucleus of the atom. They attract each other because they are of opposite charge. There is a name for the force of attraction between oppositely charged particles; it is called the electromagnetic force. This is one of the three forces that I mentioned above. The nucleus of the atom is not just comprised of protons though. In most atoms, neutrons are also present in the nucleus. The neutron, as the name might suggest, has no charge i.e. it is neutral. This means that it is not affected by the electromagnetic force. However there is a force at play that keeps the nucleus of the atom together (remember the protons and the neutrons make up the nucleus). This force is called the strong nuclear force. So we know that the strong nuclear force is what keeps protons and neutrons together, but does it do anything else? In fact, it does.
First I’m going to write down the definition of an elementary particle:
An elementary particle is a particle that is not known to have any substructure.
Basically this means that we cannot break elementary particles down any further than they already are i.e. they are indivisible. Atoms were once thought to be indivisible but we now know that we can divide them into protons, electrons and neutrons. Similarly, we have found that protons and neutrons can be broken down into simpler, smaller particles. This means that protons and neutrons are not elementary particles. These particles are known as quarks. Now, back to the strong nuclear force: As I said, the strong nuclear also has another job. That job is to hold quarks together within protons and neutrons.
I have yet to talk about the third force involved in the standard model. It is called the weak nuclear force. It is fairly obvious from the name that it is weaker than the strong nuclear force and that it is also involved in the goings-on of the nucleus of the atom. The weak nuclear force is what makes radioactive decay possible. Radioactive decay involves the emission of alpha, beta or gamma radiation from the nucleus (read a post about those here). It also enables the fusion of hydrogen nuclei (essentially just a proton and a neutron) to form helium nuclei during a process called nuclear fusion.
That really is just the tip of the iceberg when it comes to the standard model. Therefore I want to say a few more things about it. The standard model consists of 12 particles of matter. The names of these particles are the : Up quark (see above for mention of quarks), Down quark, strange quark, charm quark, top quark, bottom quark, electron, electron neutrino, tau, tau neutrino, muon, muon neutrino.
This all seems rather confusing and I won’t go in to a description of each. Essentially, all of the particles mentioned above are elementary particles. That is why the proton and neutron are not mentioned. In fact a proton consists of 2 up quarks and 1 down quark. Also, a neutron consists of 1 up quark and 2 down quarks. You might be wondering what the difference between all the different kinds of quarks are. The main differences between them are their charge and their mass. Here is a table of properties of the different types of quarks if you are interested: x
Now I won’t bother going into explanations of the other particles but I will mention that for each force mentioned above (weak nuclear, strong nuclear and electromagnetic), there is a force associated with it. Particles that ‘carry’ the weak nuclear force are called W and Z bosons. They ‘carry’ the force because they allow the force to interact between two particles that are not in direct contact. The particles move from one to the other, allowing the force to act between them. The particles that carry the strong force are called gluons and the particles that carry the electromagnetic force are called photons. Also, there is the (in)famous Higgs boson that gives all other elementary particles mass.
This depicts all of the particles that I have mentioned and it is a summary of the whole standard model: