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Particles are the building blocks of our universe. They come together to create matter, like atoms and molecules. Some particles, called gauge bosons, help transfer energy between other particles. One example of a gauge boson is the photon. These tiny particles play a big role in how our world works.

Particle families and classes

Particles are tiny objects that have physical properties like mass, charge, volume, and density. They can also carry energy. The smallest particles that make up matter are grouped into families, such as hadrons, leptons, and bosons. These particles make up all elements and their isotopes.

Particles are found on a microscopic scale, and they can range from molecules to subatomic particles. They play a crucial role in understanding the world around us.


Molecules are formed by chains of atoms and can have complex structures. Unlike some particles, molecules do not have an electrical charge. There are many examples of molecules, such as:

  • Water, which is made up of two hydrogen atoms and one oxygen atom.
  • Oxygen, which we breathe every day, is made up of two oxygen atoms.
  • Methane, a fuel source, is made up of one carbon atom and four hydrogen atoms.


Atoms are the fundamental building blocks of chemistry, consisting of neutrons, protons, and electrons. Atoms can have a neutral charge, and atoms of different elements have unique numbers of these particles, giving each element its distinctive characteristics.

The nucleus of an atom contains protons and neutrons, while electrons move around the nucleus. Together, these particles determine the chemical properties of an atom and how it interacts with other atoms.

An atom, with protons and neutrons displayed in green and the orbiting electrons in red
Figure 1. An atom, with protons and neutrons displayed in green and the orbiting electrons in red

There are many elements that make up the world around us, each with its unique properties and uses. Here are some examples:

  • Hydrogen (H): With an atomic number of 1, hydrogen is the most abundant element in the universe.
  • Carbon (C): With an atomic number of 6, carbon is the building block of all known life and reactions that made.
  • Copper (Cu): With an atomic number of 29, copper is a vital component of modern technology due to its conductivity.
  • Silicon (Si): With an atomic number of 14, silicon makes up 30% of the Earth's crust and is used to produce computer chips and construction materials.


Elements can have different isotopes when they have varying numbers of neutrons and protons. These isotopes can occur naturally or be produced in labs. One example of an element with multiple isotopes is hydrogen, which has three natural isotopes:

  • Protium: This is the most common isotope of hydrogen, with one electron and one proton.
  • Deuterium: This isotope has one electron, one proton, and one neutron, making it slightly heavier than protium.
  • Tritium: This isotope has one electron, one proton, and two neutrons, making it even heavier than deuterium. Tritium is radioactive and has a half-life of about 12 years.

Isotopes can have various physical and chemical properties, making them useful in a range of applications such as medical imaging, radiometric dating, and nuclear power generation.

The isotopes of protium, deuterium, and tritium (from left to right)
The isotopes of protium, deuterium, and tritium (from left to right)

Classical subatomic particles

Classical atomic theory describes atoms as being composed of three subatomic particles: electrons, protons, and neutrons. Protons are positively charged and are located in the nucleus of an atom along with neutrons, which are neutral. Electrons, which are negatively charged, orbit the nucleus. Photons, which are massless particles, are responsible for electromagnetic waves such as light.

In the 20th century, new particles were discovered, including the positively charged electron or "positron," which was the first proof of antimatter. These discoveries led to the classification of particles into families known as leptons, hadrons, and bosons. Leptons, such as electrons and neutrinos, are not affected by the strong nuclear force, while hadrons, such as protons and neutrons, are affected by it. Bosons are responsible for three of the four fundamental forces in the universe: electromagnetism, the weak nuclear force, and the strong nuclear force.

Radioactive decay can emit particles such as alpha particles, which are composed of two neutrons and two protons, and beta particles, which are high-velocity electrons that can be positive or negative.

Overall, particles come in different sizes and types, each with their unique properties and functions. Understanding particles is crucial in fields such as physics, chemistry, and nuclear energy.


What is a particle?

Particles in physics and chemistry refer to localised microscopic objects that can have physical properties like charge, mass, velocity, energy, etc.

How are particles formed?

Particles can consist of other particles, as in the case of neutrons and protons, which are made of quarks. Others, such as photons, electrons, or quarks, do not consist of other particles.

What is an alpha particle?

Alpha particles, which are composed of two electrons and two protons, are a source of radiation.

What is particle theory?

Particle theory predicts the energy of particles and what kinds of particles can exist.

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