Subatomic Particles You Should Know

Elementary and Subatomic Particles

The atom is the smallest particle of matter than cannot be divided using a chemical means, but atoms consist of smaller pieces, called subatomic particles. Breaking it down even further, the subatomic particles often consist of elementary particles. Here's a look at the three major subatomic particles in an atom, their electrical charges, masses, and properties. From there, learn about some key elementary particles.

Protons

The most basic unit of an atom is the proton because the number of protons in an atom determines its identity as an element. Technically, a solitary proton can be considered an atom of an element (hydrogen, in this case).

Net Charge: +1

Rest Mass: 1.67262 × 10⁻²⁷ kg

Neutrons

The atomic nucleus consists of two subatomic particles that are bonded together by the strong nuclear force. One of these particles is the proton. The other is the neutron. Neutrons are approximately the same size and mass as protons, but they lack a net electrical charge or are electrically neutral. The number of neutrons in an atom does not affect its identity, but does determine its isotope.

Net Charge: 0 (although each neutron consists of charged subatomic particles)

Rest Mass: 1.67493 × 10⁻²⁷ kg (slightly larger than that of a proton)

Electrons

The third major type of subatomic particle in an atom is the electron. Electrons are much smaller than protons or neutrons and typically orbit an atomic nucleus at a relatively great distance from its core. To put the electron's size in perspective, a proton is 1863 times more massive. Because the electron's mass is so low, only protons and neutrons are considered when calculating the mass number of an atom.

Net Charge: -1

Rest Mass: 9.10938356 × 10⁻³¹ kg

Because the electron and proton have opposite charges, they are attracted to each other. It's also important to note the charge of an electron and a proton, while opposite, are equal in magnitude. A neutral atom has an equal number of protons and electrons.

Because electrons orbit around atomic nuclei, they are the subatomic particles that affect chemical reactions. Loss of electrons can lead to the formation of positive-charged species called cations. Gaining electrons can yield negative species called anions. Chemistry is essentially the study of electron transfer between atoms and molecules.

Elementary Particles

Subatomic particles may be classified as either composite particles or elementary particles. Composite particles are made up of smaller particles. Elementary particles cannot be subdivided into smaller units.

The Standard Model of physics includes at least:

• 6 flavors of quarks: up, down, top, bottom, strange, charge
• 6 kinds of leptons: electron, muon, tau, electron neutrino, muon neutrino, tau neutrino
• 12 gauge bosons, which include the photon, 3 W and Z bosons, and 8 gluons
• Higgs boson

There are other proposed elementary particles, including the graviton and magnetic monopole.

So, the electron is a subatomic particle, an elementary particle, and a type of lepton. A proton is a subatomic composite particle made up of two up quarks and one down quark. A neutron is a subatomic composite particle consisting of two down quarks and one up quark. 

Hadrons and Exotic Subatomic Particles

Composite particles can be divided into groups, too. For example, a hadron is a composite particle made up of quarks that are held together by the strong force in much the same way as protons and neutrons bind together to form atomic nuclei.

There are two main families of hadrons: baryons and mesons. Baryons consist of three quarks. Mesons consist of one quark and one anti-quark. In addition, there are exotic hadrons, exotic mesons, and exotic baryons, which don't fit the usual definitions of the particles.

Protons and neutrons are two types of baryons, and thus two different hadrons. Pions are examples of mesons. Although protons are stable particles, neutrons are only stable when they are bound in atomic nuclei (half-life of about 611 seconds). Other hadrons are unstable.

Even more particles are predicted by supersymmetric physics theories. Examples include neutralinos, which are superpartners of neutral bosons, and sleptons, which are superpartners of leptons.

Also, there are antimatter particles corresponding to the matter particles. For example, the positron is an elementary particle that is the counterpart to the electron. Like an electron, it has a spin of 1/2 and an identical mass, but it has an electrical charge of +1.