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Particle families and classes
Particles are minuscule objects that have physical properties like mass, charge, volume, and density and can also carry energy. The most basic particles that make up matter can be divided into families, such as hadrons, leptons, and bosons. They compose all elements and their isotopes.
Particles are localized objects that can be defined on a microscopic scale, and they cover everything from molecules to subatomic particles.
Molecules
Molecules are particles that are formed from chains of atoms. The constitution of molecules can vary, and they can have very complex structures. Molecules do not have an electrical charge. Examples of molecules include:
- Water, H2Owhich consists of two atoms of hydrogen and one atom of oxygen.
- Oxygen, O2 which we breathe every day, consists of two oxygen atoms.
- Methane, CH4 which is used as fuel, consists of four hydrogen atoms and one carbon atom.
Atom
Atoms, the basic blocks of chemistry, are the smaller units of matter that can have a neutral charge. Atoms of different chemical elements have different numbers of neutrons, protons, and electrons, which gives them their distinctive properties.
Protons and neutrons are the particles that exist in the atom's nucleus. Electrons move around the nucleus.
Figure 1. An atom, with protons and neutrons displayed in green and the orbiting electrons in red. Source: Manuel R. Camacho, StudySmarter.
Atoms are classified by their atomic number, which identifies the number of protons found in the nucleus. Different elements have different numbers of protons. See the following examples of atoms belonging to different elements, including their symbols and atomic numbers:
- Hydrogen, H: with an atomic number of 1, this is the most abundant element in the universe.
- Carbon, C: with an atomic number of 6, carbon is the building block of all known reactions that made life possible.
- Copper, Cu: with an atomic number of 29, copper is one of the backbones of modern technology because of its properties as an electrical conductor.
- Silicon, Si: with an atomic number of 14, silicon comprises 30% of the earth's crust and is used to make computer chips and construction materials.
Isotopes
When an element has different numbers of neutrons and protons, it is called an isotope. Isotopes occur in nature but can also be produced in laboratories. Hydrogen has three natural isotopes, as listed below:
- Protium, which has one electron and one proton.
- Deuterium, which has one electron, one proton, and one neutron.
- Tritium, which has one electron, one proton, and two neutrons.
Figure 2. The isotopes of protium, deuterium, and tritium (from left to right). Source: Manuel R. Camacho, StudySmarter.
Classical subatomic particles
In classical atomic theory, atoms are composed of three subatomic particles: electrons, protons, and neutrons, the first two of which have an electrical charge, while neutrons are neutral. The classical theory also states that there is another particle, the photon, which has no mass and is responsible for electromagnetic waves, as in light. In summary, we have:
- Protons, which are present in the atom's nucleus and have a positive charge.
- Electrons, which move around the atom's nucleus and have a negative charge.
- Neutrons, which, like protons, are present in the atom's nucleus and do not have any charge.
- Photons, which are responsible for carrying energy in the electromagnetic spectrum, including radio waves, gamma rays, UV light, visible light, etc.
Figure 3. What we perceive as sunlight is, in fact, particles called 'photons'. Source: Andrey Larin, Flickr (CC0 1.0).
New particles in the 20th century
In the first quarter of the 20th century, only a few classical atomic particles were known, but discoveries predicted electrons with a positive charge. These predictions, made by the British scientist Paul Dirac, were confirmed by American physicist Carl Anderson after studying comics rays. The positively charged electron, also known as a 'positron', was the first proof of antimatter.
The new discoveries led to a classification of particles into large groups of families known as leptons, hadrons, and bosons.
Leptons, hadrons, and atomic forces
On a subatomic scale, we now know of two other forces in addition to the gravitational and electromagnetic ones. The first of these forces acting on an atomic scale is the strong nuclear force, which is responsible for keeping particles together. The second additional force is the weak nuclear force.
Leptons, which include electrons, neutrinos, taus, and muons, are not affected by the strong force, while hadrons, which comprise protons, neutrons and mesons, are affected by it.
Bosons
Bosons are responsible for three of the four fundamental forces of the universe: electromagnetism, the weak nuclear force, and the strong nuclear force. The particle responsible for gravity has not been found and exists only in theory (graviton). In the boson family, we find the photon, the gluon, the Z boson, the W boson, and the Higgs boson.
Particles resulting from radioactive processes
There are particles that are created as part of radioactive decay where an atom emits particles as it breaks. These particles include alpha particles and beta particles:
- Alpha particles: composed of two neutrons and two protons, they form the helium nucleus.
- Beta particles: composed of high-velocity electrons, they can be positive or negative (antimatter).
Particles - Key takeaways
- Particles are localized objects that have physical properties like mass, charge, volume, and density and can carry energy.
- Particles come in different sizes, from large molecules made of many atoms linked together to atoms and smaller subatomic particles. These subatomic particles, which compose the atom, can be divided into hadrons, leptons, and bosons.
- Bosons are the particles responsible for the exchange of three of the four fundamental forces in the universe: the electromagnetic force, the strong nuclear force, and the weak nuclear force.
- The classical subatomic particles are protons, neutrons, electrons, and photons.
- Particles can be emitted as part of radioactive processes such as radioactive decay. Examples of particles released in that way are alpha and beta particles.
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Frequently Asked Questions about Particles
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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