http://www.ck12.org Chapter 2. Matter
Leptons and Quarks and Bosons, Oh My!
Today, scientists think that electrons truly are fundamental particles that cannot be broken down into smaller, simpler
particles. They are a type of fundamental particles called leptons. Protons and neutrons, on the other hand, are no
longer thought to be fundamental particles. Instead, they are now thought to consist of smaller, simpler particles of
matter called quarks. Scientists theorize that leptons and quarks are held together by yet another type of fundamental
particles called bosons. All three types of fundamental particles—leptons, quarks, and bosons—are described below.
The followingFigure2.61 shows the variety of particles of each type.
FIGURE 2.61
- There are six types ofquarks. In ordinary matter, virtually all quarks are of the types called up and down
quarks. All quarks have mass, and they have an electric charge of either +2/3 or -1/3. For example, up quarks
have a charge of +2/3, and down quarks have a charge of -1/3. Quarks also have a different type of charge,
called color charge, although it has nothing to do with the colors that we see. Quarks are never found alone
but instead always occur in groups of two or three quarks. - There are also six types of leptons, including electrons. Leptons have an electric charge of either -1 or 0.
Electrons, for example, have a charge of -1. Leptons have mass, although the mass of electrons is extremely
small. - There are four known types of bosons, which are force-carrying particles. Each of these bosons carries a
different fundamental force between interacting particles. In addition, there is a particle which may exist,
called the "Higgs Boson", which gives objects the masses they have. Some types of bosons have mass; others
are massless. Bosons have an electric charge of +1, -1, or 0.
Q:Protons consist of three quarks: two up quarks and one down quark. Neutrons also consist of three quarks: two
down quarks and one up quark. Based on this information, what is the total electric charge of a proton? Of a neutron?
A:These combinations of quarks give protons a total electric charge of +1 (2/3 + 2/3 –1/3 = 1) and neutrons a total
electric charge of 0 (2/3 –1/3 –1/3 = 0).
Force-Carrying Particles
The interactions of matter particles are subject to four fundamental forces: gravity, electromagnetic force, weak
nuclear force, and strong nuclear force. All of these forces are thought to be transmitted by bosons, the force-