Subatomic particle

Subatomic particles are extremely small pieces of matter. These particles are smaller than, and generally parts of, atoms, the fundamental components of all known elements in the universe. The study of subatomic particles began in the late 1800s, and soon scientists, such as Ernest Rutherford and Niels Bohr, mapped the structures and particles within individual atoms. The first subatomic particles identified were protons, neutrons, and electrons, which serve in various ways to keep atoms stable and balanced. By the mid-1900s, extensive advancements in science allowed physicists to isolate and identify many new kinds of subatomic particles. Scientists George Zweig and Murray Gell-Mann proposed a theory that some types of subatomic particles are elementary, and all others are merely derivatives. Research into subatomic particles continues as scientific technology improves.

Atoms and Their Components

All objects—large or small, living or inanimate—are composed of extremely tiny particles known as atoms. These tiny building blocks combine to form chemical compounds, molecular structures, and many other forms of matter. Atoms are fundamental parts of the elements, the pure chemical substances that make up the countless features of the world. There are 109 known elements (92 occurring in nature and 17 created artificially by scientists), each of which corresponds to a unique type of atom.

Atoms share the chemical behavior of the elements they represent. They also participate in many of the occurrences that may affect elements, such as chemical reactions. Various processes involving radioactivity and the emission of energy also occur at the atomic level.

The word atom is derived from the Greek word átomos, which means indivisible. This name reflects the long-held scientific belief that atoms were the smallest and most basic level of structure, and nothing in existence could be smaller. However, modern advances in physics and other forms of research have proven that there are indeed smaller materials. These materials are called subatomic particles. Study into subatomic particles began in the late 1800s when scientific technology became advanced enough to probe individual atoms and study the particles and activities inside them.

Scientists began discovering a previously unimagined world of activity within the tiny atoms. In the early 1900s, scientists Ernest Rutherford and Niels Bohr began mapping the interiors of various atoms. The scientists developed a model of atomic structure, known as the Rutherford-Bohr model. This model revolutionized atomic study, and although it was greatly expanded upon by future generations of scientists, it remains generally accurate.

Rutherford and Bohr explained that at the center of each atom is a structure called a nucleus, which is relatively small but heavy. Inside the nucleus are two important subatomic particles known as protons and neutrons, which are collectively known as nucleons. Other subatomic particles, known as electrons, revolve around the nucleus. The Rutherford-Bohr model was strikingly similar to the arrangement of the Solar System, with small particles such as planets orbiting around a heavy central nucleus such as the Sun.

Scientists discovered that the three major subatomic particles in the Rutherford-Bohr model (proton, neutron, and electron) had their own distinct yet interrelated purposes and behaviors, which were meant to keep stability and balance within the atom. The size and number of each type of particle, the electrical charges particles emit, and the various forces pushing or pulling on particles create a unique combination of factors that define an atom and determine its behavior.

Protons are relatively large particles, about 1800 times larger than electrons, with a positive electrical charge. Neutrons are the largest of the main particles but have no electrical charge. The protons and neutrons are bundled together in the nucleus, where they are held together by the extremely powerful strong nuclear force. Any disruption of their balance, or the breaking of the strong nuclear force, can cause an atom to become unstable or radioactive.

Meanwhile, electrons are very tiny particles with a negative electrical charge. Electrons stay in orbit around the nucleus because they are held by their attraction to positive protons inside the nucleus. The electrons are a very important part of the composition and behavior of an atom. If two atoms from different elements meet, chemical reactions between them will usually involve their electrons.

Other Subatomic Particles

For years, scientists believed that protons, neutrons, and electrons comprised the full range of subatomic particles. However, two new mysterious particles, existing beyond the atmosphere of the planet, came to the attention of scientists. These particles, neutrinos and positrons, introduced the possibility that many other previously undiscovered subatomic particles may exist on Earth and beyond.

Scientists employed increasingly advanced scientific knowledge and technology and, by the mid-1900s, brought about a revolution in atomic research. The discovery of nuclear fusion and fission and the invention of particle accelerators that could break atoms into their components allowed scientists to search ever deeper into atoms and their particles. Scientists also scanned for atoms that exist beyond the range of normal human perception and found many new and mysterious forms such as delta particles, epsilon particles, and sigma particles.

Twentieth-century discoveries quickly led to a list of nearly one hundred kinds of particles that some scientists referred to as a particle zoo. The sheer abundance of such particles led many scientists to question the origins and purposes of these objects. In 1964, scientists George Zweig and Murray Gell-Mann proposed that most particles were just derivatives created by combinations of fundamental particles known as quarks and leptons.

Zweig, Gell-Mann, and many other physicists continued to research quarks, leptons, and other kinds of particles and how they combine into different forms of matter. This research has brought many insights into the behavior of atoms and subatomic particles. For instance, scientists have identified various extremely tiny particles that serve to transmit electromagnetic or gravitational energy within atoms, or bind together other parts of atoms. Study into atoms continues, with new developments greatly expanding scientific understandings of these microscopic yet essential structures.

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