What particles exist?

The known different kinds of elementary particle are three charged leptons (electron, muon, tau lepton); three neutral leptons, much more commonly called neutrinos (electron neutrino, muon neutrino, tau neutrino); six quarks (up, down, strange, charm, bottom or beauty, top); photon, W boson, Z boson, gluon, and Higgs boson. According to the current theory, there are three different kinds of each type of quark and eight different kinds of gluon. These are not strictly distinguishable experimentally even in principle. This is because the property that sets them apart (called colour) is hidden from observation. Therefore, one often simply speaks about e.g. "up quarks", "top quarks", and "gluons" without further distinction.

When we say elementary particles, this always refers to our current understanding. Many particles were once thought to be elementary before it was found out that they consist of other things. Nobody knows if there really are elementary particles, or if nature has an infinity of layers of ever "smaller" particles. No experimental observations currently suggest that any of the known elementary particles are in fact composite.

Talking about size: elementary particles have no size in the usual sense. They can be thought of as point-like, singularities, infinitely small.