What explains the variety of particles we see? (Dealing with particulate nature of matter) I'm working on a class project, and have been struggling with this question for a little while. I am in chemistry, but was hoping I'd be able to find help here as I am pretty stuck on this question.
I've been reading through my textbook and my notes, but I am not really finding anything.
The full question was, "What are the particles of matter composed of, how are they classified, and what explains the variety of particles we see?"
I am still working on my answer to the first two parts, but this is what I have so far:
"Matter is anything that has mass and takes up space, and all matter is made up of atoms. Atoms are the smallest unit of matter that retain all of the chemical properties of an element. An atom consists of three kinds of subatomic particles: electrons, protons, and neutrons. Neutrons and protons make up the nucleus, the center of the atom, and electrons surround the nucleus in an electron cloud. Atoms are classified by the number of protons and neutrons that are found in the nucleus. 
The three states of matter are Solid, Liquid, and Gas. The particles of a solid have low kinetic energy, as they are packed tightly and therefore are unable to move around. Solids have a definite shape and volume. Particles in the liquid phase have more room to move around each other, and therefore have more kinetic energy than they would in the solid phase. Particles in a liquid are still close together, but are not being held in place. Liquids have a definite volume, but unlike solids, have an indefinite shape, because the particles have room to move around each other. Particles in the gaseous phase have high kinetic energy, because they have lots of space between them and therefore can move much more. When a gas isn’t being contained, its particles can and will spread out. If it is confined, it will expand to fill the space it is being contained in. Unlike liquids and solids, gas does not have both a definite shape and definite volume."
If there is anything I should add to my response to the first two parts, that would be extremely helpful as well.
 A: There are multiple ways of treating the question, and it depends on what the question meant to ask. The comments so far are correct, but trying to answer your questions from a physics point of view, and attempting to explain what are the truly elementary particles - those that make up the protons, neutrons and so on. 
Since you are in chemistry (I assume you mean taking a chemistry class in HS) there is another possibility - that it refers to the different kinds of atoms, their properties and what those depend on, and how they combine to form molecules with even more varied and different properties. That is what chemistry mostly deals with. In that the different states such as solid, liquid and gaseous, which you already answered, becomes important. The explanation of all of that overlaps with physics, and sometimes the explanation of chemical properties using physics is called physical chemistry. For physical chemistry, the physics involved is mainly quantum mechanics, and deals with how the electrons around the atoms (or on combined atoms forming molecules) behave and interact with those of other atoms or molecules. It comes down to the properties of the different orbits around the atom (and these orbits are quantum things, often defined and best understood in terms of their quantum states). The outermost electrons in atoms tend to define the way atoms (i.e., their electrons) interact. Those electrons are said to be in the valence shell. Since shells tend to repeat above a full she'll, the atomic properties tend to be somewhat periodic.  See the wiki article on the periodic table at https://en.m.wikipedia.org/wiki/Periodic_table. 
But if one studies those atoms at higher energies, and specifically tries to understand the nucleuses, and their protons and neutrons, we get into nuclear physics, and it's about how protons and neutrons can form stable elements, and also radioactive ones (not so stable). So the particles of concern then are neutrons and protons. When one starts looking at those it turns out here are other particles that are similar, but different, eg the pions. So we needed to get inside neutrons, protons and pions and others and see what they are made up of. We did, and discovered quarks and gluons, and the so called weak and strong force. For that we used first relativistic quantum mechanics, and then quantum field theory. We now have a so called standard model (SM) that denotes the truly elementary particles we know now (but modern day physics is trying to figure out what those are made of, so at each level we try to go lower. We have not figured this deeper level yet). You can see the SM summary at Wikipedia at https://en.m.wikipedia.org/wiki/Standard_Model. 
It's almost like the periodic table, except it is not periodic at all, has different particles, and we still don't know their strucure. We do know a lot of their properties, having measured and observed them for decades. Something you may notice is what the figure labels as three different generations of fermions, 1, 2 and 3. We still don't know why there are 3, most of what we see and make up matter is one generation. The fermions make up the matter, the particles in orange, 4 of them, make up the forces like electromagnetic and strong and weak, and one of the particles, the Higgs, actually gives mass to the elementary particles. 
So, you see, the question of what are the constituents of matter depends on the level you look at it from. They are all valid, one just need to explain them all or specify the question a little more. 
As many of the comments explained, it's hard to do all this from just one chemistry course. There's more and we hope you become interested and dig into them, and ask more questions.   
