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Isotope

Isotope

Isotopes are two forms of an element with the same atomic number but different mass number. The existence of isotopes can be understood by reviewing the structure of atoms.

All atoms contain three kinds of basic particles: protons, neutrons, and electrons. (Hydrogen is the only exception to this statement; most hydrogen atoms contain no neutrons.) The protons and neutrons in an atom are found in the atomic nucleus, while the electrons are found in the space around the nucleus.

The number of protons in a nucleus defines an atom. Hydrogen atoms all have one proton in their nucleus; helium atoms all have two protons in their nucleus; lithium atoms all have three protons in their nucleus; and so on. The number of protons in an atom's nucleus is called its atomic number. Hydrogen has an atomic number of 1; helium, an atomic number of 2; and lithium, an atomic number of 3.

But atoms of the same element can have different numbers of neutrons. Some helium nuclei, for example, have two neutrons; others have only one. The mass number of an atom is the total number of protons and neutrons in the atom's nucleus. The two-neutron atom of helium has a mass number of four (two protons plus two neutrons). The one-neutron atom of helium has a mass number of three (two protons plus one neutron).

Another way of defining isotopes, then, is to say that they are different forms of an atom with the same number of protons but different numbers of neutrons.

Most elements have at least two stable isotopes. The term stable here means not radioactive. Twenty elements, including fluorine, sodium, aluminum, phosphorus, and gold, have only one stable isotope. By contrast, tin has the largest number of stable isotopes of any element, ten.

Representing isotopes

Isotopes are commonly represented in one of two ways. First, they may be designated by writing the name of the element followed by the mass number of the isotope. The two forms of helium are called helium-4 and helium-3. Second, isotopes may be designated by the chemical symbol of the element with a superscript that shows their mass number. The designations for the two isotopes of helium are 4He and 3He.

Radioactive isotopes

A radioactive isotope is an isotope that spontaneously breaks apart, changing into some other isotope. As an example, potassium has a radioactive isotope with mass number 40, 40K or potassium-40. This isotope breaks down into a stable isotope of potassium, 39K or potassium-39.

Radioactive isotopes are much more common than are stable isotopes. At least 1,000 radioactive isotopes occur in nature or have been produced synthetically in particle accelerators (atom-smashers) or nuclear reactors (devices used to control the release of energy from nuclear reactions).

Applications

Isotopes have many important applications in theoretical and practical research. The advantage of using two or more isotopes of the same element is that the isotopes will all have the same chemical properties but may differ from each other because of their mass differences. This difference allows scientists to separate one isotope from another. An important example of this process is the way isotopes were used to purify uranium during World War II (193945).

Two common isotopes of uranium exist, 235U and 238U. Of these two, 238U is much more abundant, making up about 99.3 percent of the uranium found in nature. But only 235U can be used in making nuclear weapons and nuclear reactors. Since both 235U and 238U have the same chemical properties, how can the valuable 235U be separated from the more abundant, but valueless, 238U?

One answer to this question was to convert natural uranium to a gas and then allow the gas to diffuse (spread out) through a porous barrier. Researchers found that the 235U in the natural uranium was slightly less heavy than the 238U, so it diffused through the barrier slightly more quickly. But because the difference in mass between the two isotopes is not very great, the diffusion had to be repeated many times before the two isotopes could be separated very well. Eventually, however, enough 235U was collected by this process to make the world's first nuclear weapons.

[See also Atomic mass; Carbon family; Dating techniques; Nuclear fission; Nuclear medicine; Periodic table; Radioactive tracers; Radioactivity; Spectrometry ]

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isotope

isotope One of two or more varieties of a chemical element whose atoms have a common number of protons and electrons (i.e. their atomic number is the same) but which vary in the number of neutrons in their nucleus (i.e. their atomic weight, signified by their mass number, is different). For example, hydrogen exists in the forms 11H (one proton, no neutron), 21H (deuterium: one proton, one neutron), and 31H (tritium: one proton, 2 neutrons). Water in which 21H replaces the more common 11H is known as ‘heavy water’. There are 300 naturally occurring isotopes, but only 92 naturally occurring elements, and in nature elements often occur as a mixture of isotopes, with one form being the most common. Isotopes may be produced by various nuclear reactions and the products are frequently radioactive. There are three different ways of specifying an isotope; for example 235U, U-235, and uranium 235 all indicate the isotope of uranium with a mass number of 235. See also ISOTOPIC DATING.

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isotope

i·so·tope / ˈīsəˌtōp/ • n. Chem. each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties; in particular, a radioactive form of an element. DERIVATIVES: i·so·top·ic / ˌīsəˈtäpik/ adj. i·so·top·i·cal·ly / ˌīsəˈtäpik(ə)lē/ adv. i·sot·o·py / ˈīsəˌtōpē; īˈsätəpē/ n.

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isotope

isotope One of two or more atoms with the same atomic number but a different number of neutrons. Both mass number and mass of the nucleus are different for different isotopes. The atomic mass of an element is an average of the isotope masses. The isotopes of an element have similar chemical properties, but physical properties vary slightly. Most elements have two or more naturally occurring isotopes, some of which are radioactive (radioisotopes). Hydrogen, for example, has two isotopes, deuterium and the radioactive tritium. Radioisotopes are used in medicine, research and industry. Radioactive dating also uses isotopes.

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isotope

isotope (I-sŏ-tohp) n. any one of the different forms of an element, having the same atomic number but different atomic weights. Radioactive isotopes decay into other isotopes or elements, emitting alpha, beta, or gamma radiation. Artificially produced radioactive isotopes are used extensively as tracers (see also gamma camera, scintigram) and in radiotherapy for the treatment of cancer.

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isotope

isotope One of two or more varieties of a chemical element whose atoms have the same numbers of protons and electrons but different numbers of neutrons. There are 300 naturally occurring isotopes, but only 92 naturally occurring elements. Isotopes may be produced by various nuclear reactions. Frequently the products are radioactive. See also isotopic dating.

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"isotope." A Dictionary of Ecology. . Retrieved August 22, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/isotope-0

isotope

isotope One of 2 or more varieties of a chemical element whose atoms have the same numbers of protons and electrons but different numbers of neutrons. There are 300 naturally occurring isotopes, but only 92 naturally occurring elements. Isotopes may be produced by various nuclear reactions. Frequently the products are radioactive. See also ISOTOPIC DATING.

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isotope

isotope XX. f. ISO- + Gr. tópos place (i.e. in the periodic table of elements).

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"isotope." The Concise Oxford Dictionary of English Etymology. . Encyclopedia.com. 22 Aug. 2017 <http://www.encyclopedia.com>.

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isotope

isotopeaslope, cope, dope, elope, grope, hope, interlope, lope, mope, nope, ope, pope, rope, scope, slope, soap, taupe, tope, trope •myope • telescope • periscope •stereoscope • bioscope • stroboscope •kaleidoscope • CinemaScope •gyroscope • microscope • horoscope •stethoscope • antelope • envelope •zoetrope • skipping-rope • tightrope •towrope • heliotrope • lycanthrope •philanthrope • thaumatrope •misanthrope •isotope, radioisotope

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