Matter is made up of atoms that are composed of small particles. These small particles are the building block of atoms called subatomic particles. They are further divided into elementary particles and composite particles. The elementary particles cannot be separated further however, composite particles are the combination of two or more elementary particles.
An atom is a sum of elementary and composite subatomic particles. For example, the electron is an elementary particle whereas a proton and neutron are composite particles. They combine to give a whole structure of the atom.
Subatomic particles that are found in the nucleus
Sub-atomic particles in the nucleus of an atom are called nucleons. Nucleons are composite sub-atomic particles that are made up of elementary particles.
These are the subatomic particles in a nucleus:
Proton
Protons are the basic unit of an atom. They give an identity to the atom and are composite subatomic particles. In addition to it, they are made up of quarks, two up quarks and one down quark which are elementary subatomic particles.
It is to be noted that the net charge of a proton is +1 and its rest mass is 1.67262 x 10-27kg.
Neutron
Neurons are also composite subatomic particles that are formed by the combination of quarks. There are two down quarks and one up quark combined to give a neutron. They have a similar size and mass as the protons but with no charge. That means neutrons are electrically neutral.
Neutron has a slightly larger rest mass of 1.67493 x 10-27 kg than proton.
Subatomic particles which participate in chemical bonding
Due to weak or strong forces, elementary sub-atomic particles are responsible for chemical bonding. The electron has a negative charge and only participates in the chemical bonds. Electrons are much smaller than protons or neutrons. Proton is about 1863 times more massive than electrons.
Due to small mass, size, and negative charge, electrons always revolve around the nucleus in an orbit. The electron has a net charge of -1 and a rest mass of 9.10938356 x 10-31 kg. Electrons and protons have opposite charges when there is an equal number of protons and electrons present in an atom called a neutral atom. This is because they cancel the charge effect of each other.
Elementary sub-atomic particles
Elementary subatomic particles are the very basic particles that act as starting particles for the formation of composite subatomic particles. These are the basic elementary subatomic particles listed below:
Quarks
These are the six types of quarks listed below:
- Up quark (u)
- Down quark (d)
- Strange quark (s)
- Charm quark (c)
- Top quark (t)
- Bottom quark (b)
Up and down quarks have the lowest masses of all of the quarks. However, heavier quarks are transformed into up-and-down quarks by decaying. This is a reason, up and down quarks are very stable and occur everywhere in the universe. As compared to up and down quarks, other quarks like the top, bottom, charm, and strange are only formed during high-energy collisions.
Every quark has its opposite quark called an antiparticle or antiquark. This has opposite properties to quarks like antiquark has a negative charge while a quark has a positive charge.
Leptons
These are the six types of leptons:
- Electron (e−)
- Electron neutrino (νe)
- Muon (μ−)
- Muon neutrino (νμ)
- Tau (τ−)
- Tau neutrino (ντ)
Electron, muon, and tau are charged elementary sub-atomic particles and can be combined to form composite subatomic particles. Whereas neutrinos are neutral and rarely combine with other particles.
Gauge bosons
These are twelve gauge bosons that are force carriers. W and Z bosons are weak force carriers while gluons are strong force carriers.
- Photon (γ)
- Three W and Z bosons (W+, W–, Z0)
- Eight gluons (g)
Gauge bosons are elementary subatomic particles that play an important role as a force carrier for elementary fermions. These elementary particles interact with each other with the help of exchange gauge bosons. In this way, they act as virtual particles and have a spin of 1. Additionally, they are also known as vector bosons.
Higgs bosons
They are also called scalar bosons due to zero spin and have no charge, no color, and positive parity with the (H) symbol. Higgs bosons are very unstable and transform into other particles.
Composite subatomic particles
Composite subatomic particles are made up of more than one elementary particle. For example, almost every composite subatomic particle is formed by the combination of multiple quarks and/or antiquarks with the help of gluons except some of them like positronium and muonium, etc.
Hadrons
One of the best examples of composite sub-atomic particles is hadron. Hadrons are the combination of less than or equal to five quarks or antiquarks bound together with the help of gluons. On the basis of the number of quarks or antiquarks, they are classified into two categories:
Baryons
They have odd numbers of quarks like 3. For example, protons and neutrons are made up of baryons. Proton is formed by the combination of two up quarks and one down quark. On the other hand, neutrons are formed by the two down quarks and one up quarks.
Mesons
They have even numbers of quarks like 2. One is quark and the second is antiquark. Pions and kaons are examples of mesons.
All hadrons are very unstable except protons and neutrons. They can easily decay into other particles in a few microseconds. Note that, protons and neutrons collectively formed a nucleus.
Classification of subatomic particles
Sub-atomic particles are further classified into three categories given below:
On the basis of statistics
In 3d space, subatomic particles obey the law of quantum mechanics. They act as bosons or fermions. Bosons have integer spin while all the elementary fermions have a spin of ½. Further, fermions are divided into quarks that provide strong interaction due to color charge whereas leptons do not. Gauge bosons such as photons, Z and W bosons, and gluons have a spin of 1, and the Higgs boson is the only particle with a spin of 0.
On the basis of mass
According to Einstein’s equation, the energy (E) of a particle is equal to its mass (m) and the square of the speed of light (c2).
E = mc2
The energy and mass of the particle are directly proportional which means mass is expressed in the term of energy. When this particle is at rest at any point called its frame of reference and the particle has a positive rest mass known as massive.
All massive particles are composite subatomic particles while massless particles are elementary subatomic particles.
- Baryons have heavier masses than mesons.
- Mesons are heavier than leptons.
- Tau particles are heavier than protons and neutrons.
Before the acceptance of the quark model 1970s, the terms baryons, mesons, and leptons are considered for masses. Later it is found that baryons have three quarks, mesons have one quark and one antiquark whereas leptons are elementary sub-atomic particles.
On the basis of decay
Sub-atomic particles are not stable except for protons and neutrons. They can transform from one particle to another by the process of decay.
- All leptons and baryons decay by strong forces as well as weak forces.
- Muons have also their antiparticles and decay by weak forces.
- Neutrinos and antineutrinos cannot decay.
- Electrons and positrons are theoretically stable.
Related Resources
- Atom vs. Molecule: Key Points, Explanation, and Examples
- Rutherford Atomic Model
- Dalton’s Atomic Theory: History, Postulates, Limitations
- Atomic Mass vs. Molar Mass: The Basic Concepts of Chemistry
Concepts Berg
What is an atom?
An atom is the smallest particle that made up the whole structure of matter. They are the structural and functional units of matter. For instance, an atom is made up of subatomic particles like elementary sub-atomic particles and composite subatomic particles.
How is a subatomic particle made?
There are two types of subatomic particles. One is the elementary sub-atomic particles that are isolated particles and the second type of subatomic particles are composite subatomic particles that are made up of elementary subatomic particles.
What are the 7 particles of an atom?
These are three types of main particles that are further divided into particles:
- Electron (itself an elementary subatomic particle)
- Proton (made by 2 up quarks and 1 down quark)
- Neutron (made by 2 down quarks and 1 up quark)
In this way, there are seven subatomic particles are involved in the formation of an atom.
Do sub-atomic particles really exist?
Sub-atomic particles exist but they are unstable. There are only a few exceptions that are stable like elementary subatomic particles and protons, and neutrons from composite subatomic particles.
what is the difference between subatomic particles and quarks?
Quarks are subatomic particles that exist in an isolated form called elementary subatomic particles. They are not divisible. On the other hand, composite subatomic particles are divisible.
References
- What is an atom (NRC.org)
