Proton
Proton
The proton is a positively charged subatomic particle. Protons are one of the fundamental constituents of all atoms. Protons, in addition to neutrons, are found in a very concentrated region of space within atoms referred to as the nucleus. The discovery of the proton, neutron, and electron revolutionized the way scientists viewed the atom. Recent research has shown that protons are themselves made up of even smaller particles called quarks and gluons.
History and discovery
Early atomic theory assumed that atoms were indivisible. However, when English physicist and chemist Michael Faraday (1791–1867) demonstrated, in 1834, that chemical elements were electrical in nature, scientists embarked on a series of experiments that challenged, and eventually demolished, the fundamental assumptions of traditional atomic theory. For example, in 1878, British chemist and physicist Sir William Crookes (1832–1919), who predicted the discovery of isotopes, started experimenting with cathode rays, which occurred when electricity was discharged between two metal plates in a tube (later named a Crookes tube) with gas at an extremely low pressure. Crookes believed these rays were negatively charged electrons. In 1897, however, English physicist J. J. Thomson (1856–1940) identified them as subatomic particles, eventually named electrons. Further experiments led to the discovery of protons. For example, when scientists drilled holes in the positively charged (anode) plate of the Crookes tube, they detected rays moving in the opposite direction (from the anode to the negatively charged cathode) of the cathode rays. Named canal rays, these rays were studied by German physicist Wilhelm Wien (1864– 1928). In 1905, Wien identified some of these rays are hydrogen ions. Researchers later established that rays with the least mass were protons.
In 1909, New Zealand-British physicist Ernest Rutherford (1871–1937) instructed his younger colleague German nuclear physicist Hans Geiger (1882– 1945) and German physicist and inventor Ernst Marsden (1889–1970), who was still an undergraduate, to perform the gold foil experiment. The experimenters bombarded a thin gold foil with alpha particles (helium atoms without electrons). Since the current model of the atom was a positively charged sphere (pudding) with negative globs (plums) inserted throughout (the plum pudding model), they expected the alpha particles to penetrate the foil without resistance. Indeed, most of the alpha particles did, but a small number were strongly repelled. These results indicated that the gold atom had a positively charged nucleus. In 1919, Rutherford identified the proton as the fundamental unit of positive electrical charge in the atom. The neutron, the major particle constituting the atom’s nucleus
KEY TERMS
Atomic number— The number of protons in the nucleus of an atom.
Gluons— Subatomic particles that help to keep quarks bound together.
Quarks— Believed to be the most fundamental units of protons and neutrons.
Radioactivity— Spontaneous release of subatomic particles or gamma rays by unstable atoms as their nuclei decay.
was discovered in 1932 by English physicist James Chadwick (1891–1974). Approximately equal to a proton in mass, the neutron has no charge.
Properties
The proton’s mass and charge have both been determined. The mass is 1.673 x 10-24 g. The charge of a proton is positive, and is assigned a value of +1. The electron has a -1 charge, and is about 2,000 times lighter than a proton. In neutral atoms, the number of protons and electrons are equal.
The number of protons (also referred to as the atomic number) determines the chemical identity of an atom. Each element in the periodic table has a unique number of protons in its nucleus. The chemical behavior of individual elements largely depends, however, on the electrons in that element. Chemical reactions involve changes in the arrangements of electrons, not in the number of protons or neutrons.
The processes involving changes in the number of protons are referred to as nuclear reactions. In essence, a nuclear reaction is the transformation of one element into another. Certain elements—both natural and artificially made—are by their nature unstable, and spontaneously break down into lighter elements, releasing energy in the process. This process is referred to as radioactivity. Nuclear power is generated by just such a process.
Inner structure
Research has shown the proton to be made up of even smaller constituent particles. A proton is found to consist of two up quarks, each with a +2/3 electric charge, and one down quark, with a -1/3 electric charge. The individual quarks are held together by particles called gluons. The up and down quarks are currently believed to be two of the three fundamental particles of all matter. Recent research has revealed the possibility of an even deeper substructure, and further work could lead to new theories that may overturn the current model of the proton’s structure. Scientists are continuing to use high-energy beams from within particle accelerators to discover more complex information about protons.
See also Subatomic particles.
Resources
BOOKS
Blaschke, D., M.A. Ivanov, and T. Mannel, eds. Heavy Quark Physics. Berlin, Germany: Springer, 2004.
Folan, Lorcan M. Modern Physics and Technology for Undergraduates. River Edge, NJ: World Scientific, 2003.
Staley, Kent W. The Evidence for the Top Quark: Objectivity and Bias in Collaborative Experimentation. Cambridge, UK, and New York: Cambridge University Press, 2004.
Taylor, John Robert. Modern Physics for Scientists and Engineers. Upper Saddle River, NJ: Pearson Prentice Hall, 2004.
Young, Hugh D. Sears and Zemansky’s University Physics. San Francisco, CA: Pearson Addison Wesley, 2004.
Michael G. Roepel
Proton
Proton
The proton is a positively charged subatomic particle. Protons are one of the fundamental constituents of all atoms . Protons, in addition to neutrons, are found in a very concentrated region of space within atoms referred to as the nucleus. The discovery of the proton, neutron , and electron revolutionized the way scientists viewed the atom. Recent research has shown that protons are themselves made up of even smaller particles called quarks and gluons.
Discovery and properties
Prior to the late nineteenth and early twentieth centuries, scientists believed that atoms were indivisible. Work by many scientists led to the nuclear model of the atom, in which protons, neutrons, and electrons make up individual atoms. Protons and neutrons are found in the nucleus, while electrons are found in a much greater volume around the nucleus. The nucleus represents less than 1% of the atom's total volume.
The proton's mass and charge have both been determined. The mass is 1.673 × 10-24 g. The charge of a proton is positive, and is assigned a value of +1. The electron has a –1 charge, and is about 2,000 times lighter than a proton. In neutral atoms, the number of protons and electrons are equal.
The number of protons (also referred to as the atomic number ) determines the chemical identity of an atom. Each element in the periodic table has a unique number of protons in its nucleus. The chemical behavior of individual elements largely depends, however, on the electrons in that element. Chemical reactions involve changes in the arrangements of electrons, not in the number of protons or neutrons.
The processes involving changes in the number of protons are referred to as nuclear reactions. In essence, a nuclear reaction is the transformation of one element into another. Certain elements—both natural and artificially made—are by their nature unstable, and spontaneously break down into lighter elements, releasing energy in the process. This process is referred to as radioactivity. Nuclear power is generated by just such a process.
Inner structure
Research has shown the proton to be made up of even smaller constituent particles. A proton is found to consist of two "up" quarks, each with a +2/3 electric charge , and one "down" quark, with a -1/3 electric charge. The individual quarks are held together by particles called gluons. The up and down quarks are currently believed to be two of the three fundamental particles of all matter. Recent research has revealed the possibility of an even deeper substructure, and further work could lead to new theories which may overturn the current model of the proton's structure.
See also Subatomic particles.
Resources
books
Baeyer, Hans Christian von. Rainbows, Snowflakes andQuarks. New York: Random House, 1984.
Rothman, Tony. Instant Physics. New York: Fawcett Columbine, 1995.
Trefil, James. From Atoms to Quarks. New York: Doubleday, 1980.
periodicals
Hellemans, Alexander. "Searching for the Spin of the Proton." Science 267 (March 1995): 1767.
Peterson, Ivars. "The Stuff of Protons." Science News 146 (27 August 1994): 140-41.
Michael G. Roepel
KEY TERMS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .- Atomic number
—The number of protons in the nucleus of an atom.
- Gluons
—Subatomic particles that help to keep quarks bound together.
- Quarks
—Believed to be the most fundamental units of protons and neutrons.
- Radioactivity
—Spontaneous release of subatomic particles or gamma rays by unstable atoms as their nuclei decay.
proton
proton
pro·ton / ˈprōˌtän/ • n. Physics a stable subatomic particle occurring in all atomic nuclei, with a positive electric charge equal in magnitude to that of an electron, but of opposite sign.DERIVATIVES: pro·ton·ic / prōˈtänik/ adj.