Question: What are the differences between leptons and quarks?
About the article "Electron", section "Classification".

Candidate passages:
The quantum chromodynamics (QCD) sector defines the interactions between quarks and gluons, with SU(3) symmetry, generated by "T""a".
Since leptons do not interact with gluons, they are not affected by this sector.
The Dirac Lagrangian of the quarks coupled to the gluon fields is given by :formula_160 where D and U are the Dirac spinors associated with up- and down-type quarks, and other notations are continued from the previous section. 
As seen in the above discussion, many early definitions of what can be called "ordinary matter" were based upon its structure or "building blocks".
On the scale of elementary particles, a definition that follows this tradition can be stated as: "ordinary matter is everything that is composed of elementary fermions, namely quarks and leptons."
The connection between these formulations follows.
Leptons (the most famous being the electron), and quarks (of which baryons, such as protons and neutrons, are made) combine to form atoms, which in turn form molecules.
Because atoms and molecules are said to be matter, it is natural to phrase the definition as: "ordinary matter is anything that is made of the same things that atoms and molecules are made of".
(However, notice that one also can make from these building blocks matter that is "not" atoms or molecules.)
Then, because electrons are leptons, and protons, and neutrons are made of quarks, this definition in turn leads to the definition of matter as being "quarks and leptons", which are the two types of elementary fermions.
Carithers and Grannis state: "Ordinary matter is composed entirely of first-generation particles, namely the and [down quarks, plus the electron and its neutrino."
(Higher generations particles quickly decay into first-generation particles, and thus are not commonly encountered.
)This definition of ordinary matter is more subtle than it first appears.
All the particles that make up ordinary matter (leptons and quarks) are elementary fermions, while all the force carriers are elementary bosons.
The W and Z bosons that mediate the weak force are not made of quarks or leptons, and so are not ordinary matter, even if they have mass.
In other words, mass is not something that is exclusive to ordinary matter.
The quark–lepton definition of ordinary matter, however, identifies not only the elementary building blocks of matter, but also includes composites made from the constituents (atoms and molecules, for example).
Such composites contain an interaction energy that holds the constituents together, and may constitute the bulk of the mass of the composite.
As an example, to a great extent, the mass of an atom is simply the sum of the masses of its constituent protons, neutrons and electrons.
However, digging deeper, the protons and neutrons are made up of quarks bound together by gluon fields (see dynamics of quantum chromodynamics) and these gluons fields contribute significantly to the mass of hadrons.
In other words, most of what composes the "mass" of ordinary matter is due to the binding energy of quarks within protons and neutrons.
For example, the sum of the mass of the three quarks in a nucleon is approximately , which is low compared to the mass of a nucleon (approximately ).
The bottom line is that most of the mass of everyday objects comes from the interaction energy of its elementary components. 
The Standard Model groups matter particles into three generations, where each generation consists of two quarks and two leptons.
The first generation is the "up" and "down" quarks, the "electron" and the "electron neutrino"; the second includes the "charm" and "strange" quarks, the "muon" and the "muon neutrino"; the third generation consists of the "top" and "bottom" quarks and the "tau" and "tau neutrino".
The most natural explanation for this would be that quarks and leptons of higher generations are excited states of the first generations.
If this turns out to be the case, it would imply that quarks and leptons are composite particles, rather than elementary particles. 
There is an entire literature concerning the "structure of matter", ranging from the "electrical structure" in the early 20th century, to the more recent "quark structure of matter", introduced today with the remark: "Understanding the quark structure of matter has been one of the most important advances in contemporary physics."
In this connection, physicists speak of "matter fields", and speak of particles as "quantum excitations of a mode of the matter field".
And here is a quote from de Sabbata and Gasperini: "With the word "matter" we denote, in this context, the sources of the interactions, that is spinor fields (like quarks and leptons), which are believed to be the fundamental components of matter, or scalar fields, like the Higgs particles, which are used to introduced mass in a gauge theory (and that, however, could be composed of more fundamental fermion fields).
"The modern conception of matter has been refined many times in history, in light of the improvement in knowledge of just "what" the basic building blocks are, and in how they interact.
In the late 19th century with the discovery of the electron, and in the early 20th century, with the discovery of the atomic nucleus, and the birth of particle physics, matter was seen as made up of electrons, protons and neutrons interacting to form atoms.
Today, we know that even protons and neutrons are not indivisible, they can be divided into quarks, while electrons are part of a particle family called leptons.
Both quarks and leptons are elementary particles, and are currently seen as being the fundamental constituents of matter.
These quarks and leptons interact through four fundamental forces: gravity, electromagnetism, weak interactions, and strong interactions.
The Standard Model of particle physics is currently the best explanation for all of physics, but despite decades of efforts, gravity cannot yet be accounted for at the quantum level; it is only described by classical physics (see quantum gravity and graviton).
Interactions between quarks and leptons are the result of an exchange of force-carrying particles (such as photons) between quarks and leptons.
The force-carrying particles are not themselves building blocks.
As one consequence, mass and energy (which cannot be created or destroyed) cannot always be related to matter (which can be created out of non-matter particles such as photons, or even out of pure energy, such as kinetic energy).
Force carriers are usually not considered matter: the carriers of the electric force (photons) possess energy (see Planck relation) and the carriers of the weak force (W and Z bosons) are massive, but neither are considered matter either.
However, while these particles are not considered matter, they do contribute to the total mass of atoms, subatomic particles, and all systems that contain them. 
Leptons are particles of spin-, meaning that they are fermions.
They carry an electric charge of −1 e (charged leptons) or 0 e (neutrinos).
Unlike quarks, leptons do not carry colour charge, meaning that they do not experience the strong interaction.
Leptons also undergo radioactive decay, meaning that they are subject to the weak interaction.
Leptons are massive particles, therefore are subject to gravity.