Which has the smallest particle of atom

The Ancient Greeks had a name for the smallest particle: the ‘atom’, meaning ‘not cuttable’. But ever since Ernest Rutherford famously split the atom in experiments at Cambridge University around a century ago, it’s been clear that the name is a misnomer. He found that atoms contain a central nucleus around 10,000 times smaller than the atom itself.

By the early 1960s, researchers firing electrons at atoms were finding hints that even the protons and neutrons making up atomic nuclei contain some kind of structure – now known to be quarks – trapped inside them. In the last few years, experiments at the Large Hadron Collider particle accelerator have suggested that quarks may themselves be at least 10,000 times smaller than protons and neutrons.

But there’s one subatomic particle that’s far smaller still, and not even the most powerful particle accelerator has come close to pinning down its size: the electron.

Physics textbooks sometimes mention the so-called ‘classical radius of the electron’, which – at around three-million-billionths of a metre – is similar to that of a proton. But this comes from a theory that assumes the electron is just a ball of electromagnetic energy, which isn’t really true.

A more reliable insight into its true size comes from using quantum theory, which ties the size of subatomic particles to their angular momentum (‘spin’) and their magnetic properties. In the case of the electron, measurements of these properties suggest that the electron is at least 1,000 times smaller even than quarks.

Read more:

• What shape are subatomic particles?
• Who really discovered the Higgs particle?
• How can an electron be both a particle and a wave?
• What holds together the protons and neutrons in an atom’s nucleus?

An element is a substance completely made up of one atom. Thus, the periodic table of elements is effectively a list of all known types of atoms. However, the atom itself is not the smallest known particle, but instead each atom is made up of three individual parts: electrons, protons and neutrons. Furthermore, protons and neutrons themselves are made up of even smaller parts called quarks.

Electrons

Electrons are fundamental particles, which means no particle is known to make up an electron. Electrons are what give an atom of an element its charge; you can change the number of electrons to make it a positively- or negatively-charged version of the same atom. A neutrally-charged atom will have the same amount of electrons as protons. Electrons exists in orbitals, which surround the nucleus of the atoms, and it is in these orbitals that electrons can bond with other atoms to form compounds.

Protons

Protons are the defining characteristic of an element's atom; the number of protons is what gives the atom its mass (electrons have a negligible amount of mass in comparison to protons). Thus, elements are classified by the number of protons its atoms have and organized in such a way on the periodic table (e.g., a hydrogen atom has one proton, a carbon atom has six, etc.). Protons are found in the nucleus of the atom.

Neutrons

Neutrons are about as massive as protons, and are found in the nucleus of the atom alongside protons. While protons have a positive charge and electrons have a negative charge, neutrons have no charge. Much how changing the number of electrons does not change the element itself, changing the amount of neutrons keeps relatively the same type of element, but creates an isotope. Isotopes can be unstable, and when they decay, they release energy in the form of radiation.

Quarks

Electrons are fundamental particles; however, protons and neutrons are made up of a different set of fundamental particles known as quarks. Discovered in 1961, quarks are the smallest known particles in physics, and there are six types (up, down, charm, strange, bottom and top). Three quarks combine together to form baryons, which include protons and neutrons. A quark can also combine in a pair with an antiquark to form a meson, but this type of matter is extremely unstable and lasts for only a fraction of a millisecond.

Atoms represent the smallest pieces of matter with constant properties, and are referred to as the basic unit of matter. However, scientists have discovered that atoms are not the smallest particles in nature. Despite their minuscule size, a number of much smaller particles exist, known as subatomic particles. In actuality, it is these subatomic particles that form the building blocks of our world, such as protons, neutrons, electrons and quarks, or destroy it, such as alpha and beta particles.

Protons

The proton was discovered by Earnest Rutherford in 1919. This subatomic particle is located in the nuclei of atoms. The particle’s mass is equal to approximately one atomic mass and, along with the atom’s neutrons, accounts for the majority of an atom’s overall mass. Protons have a positive charge. The atoms of every element have a set number of protons, representing the elements atomic number.

Neutrons

The neutron was discovered by James Chadwick in 1932. This subatomic particle is located in the nuclei of atoms. The particle’s mass is equal to approximately one atomic mass and, along with the atom’s protons, accounts for the majority of the atom’s overall mass. Neutrons have no electrical charge. The number of neutrons can vary for atoms of a given element, with each variation called an isotope.

Electrons

The electron was the first subatomic particle to be identified, discovered by Sir John Joseph Thomson in 1897. Electrons orbit around an atom’s nucleus in what is referred to as an electron cloud. The particle’s mass is tiny, approximately 1,840 times smaller than protons and neutrons. The subatomic particle has a negative charge. Electrons are primarily responsible for chemical interactions. Electrons in the outer orbit are lost, gained or shared with other atoms, forming chemical bonds.

Alpha Particles

Alpha particles represent the nuclei of helium atoms, comprised of two protons and two neutrons. These subatomic particles are produced by radioactive alpha decay in large, unstable atoms. These particles have relatively low energy and are unable to penetrate very deeply into other materials. However, due to their size, alpha particles can be extremely destructive to human cells that they manage to come into contact with.

Beta Particles

Beta particles represent free electrons or positrons. Positrons have the same mass as electrons, but posses a positive charge. Beta particles are produced by radioactive beta decay. They have relatively high energy and move at high speeds. Because of these properties, beta particles are able to penetrate materials around 100 times deeper than alpha particles.

Quarks

Quarks represent the smallest known subatomic particles. These building blocks of matter are considered the new elementary particles, replacing protons, neutrons and electrons as the fundamental particles of the universe. There are six types, called flavors of quarks: up, down, charm, strange, top and bottom. Furthermore, quarks come in three colors, representing their force: red, blue and green. Up and down quarks are the most common and least massive. Protons are comprised of one down and two up quarks, while neutrons are comprised of one down and two up quarks.