Isotopes are any of the different forms of an element each having different atomic mass (mass number). A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus. The mass number ( A) also called atomic mass number or nucleon number, is the total number of Protons and Neutrons (together known as Isotopes of an element have nuclei with the same number of protons (the same atomic number) but different numbers of neutrons. The nucleus of an Atom is the very dense region consisting of Nucleons ( Protons and Neutrons, at the center of an atom The proton ( Greek πρῶτον / proton "first" is a Subatomic particle with an Electric charge of one positive See also List of elements by atomic number In Chemistry and Physics, the atomic number (also known as the proton This article is a discussion of neutrons in general For the specific case of a neutron found outside the nucleus see Free neutron. Therefore, isotopes have different mass numbers, which give the total number of nucleons—the number of protons plus neutrons. The mass number ( A) also called atomic mass number or nucleon number, is the total number of Protons and Neutrons (together known as In Physics a nucleon is a collective name for two Baryons the Neutron and the Proton.

A nuclide is any particular atomic nucleus with a specific atomic number Z and mass number A; it is equivalently an atomic nucleus with a specific number of protons and neutrons. A nuclide (from lat nucleus is a species of Atom characterized by the constitution of its nucleus and hence by the number of Protons, the number of Collectively, all the isotopes of all the elements form the set of nuclides. The distinction between the terms isotope and nuclide has somewhat blurred, and they are often used interchangeably. Isotope is best used when referring to several different nuclides of the same element; nuclide is more generic and is used when referencing only one nucleus or several nuclei of different elements. For example, it is more correct to say that an element such as fluorine consists of one stable nuclide rather than that it has one stable isotope. Fluorine, fluorum meaning "to flow" is the Chemical element with the symbol F and Atomic number 9

In IUPAC nomenclature, isotopes and nuclides are specified by the name of the particular element, implicitly giving the atomic number, followed by a hyphen and the mass number (e. IUPAC Nomenclature is a system of naming Chemical compounds and of describing the science of Chemistry in general g. helium-3, carbon-12, carbon-13, iodine-131 and uranium-238). This article is about the elemental isotope For the record label Helium 3 see Muse or A&E Records. Carbon-12 is the most abundant of the two stable Isotopes of the element Carbon, accounting for 98 Carbon-13 ( 13C) is a natural stable Isotope of Carbon and one of the Environmental isotopes. Iodine-131 (131I, also called radioiodine, is a Radioisotope of Iodine which has medical and pharmaceutical uses Uranium-238 (U-238 is the most common isotope of Uranium found in nature In symbolic form, the number of nucleons is denoted as a superscripted prefix to the chemical symbol (e. This article is about the terms 'subscript' and 'superscript' as used in typography See also Chemical formula. A chemical symbol is an Abbreviation or shortened version of the name of a Chemical element g. ³He, ¹²C, ¹³C, ¹³¹I and ²³⁸U).

About 339 nuclides occur naturally on Earth, of which 269 (about 79%) are stable. ^[1] Counting the radioactive nuclides not found in nature that have been created artificially, more than 3100 nuclides are currently known. ^[2]

History of the term

In the bottom right corner of JJ Thomson's photographic plate are markings for the two isotopes of neon: neon-20 and neon-22.

The term isotope was coined in 1913 by Margaret Todd, a Scottish doctor, during a conversation with Frederick Soddy (to whom she was distantly related by marriage). Margaret Todd (1859 &ndash 1918 was a Scottish writer and doctor who in 1913 suggested the term Isotope to chemist Frederick Soddy. Frederick Soddy ( 2 September 1877 &ndash 22 September 1956) was an English radiochemist. ^[3] Soddy, a chemist at Glasgow University, explained that it appeared from his investigations as if several elements occupied each position in the periodic table. The periodic table of the chemical elements is a tabular method of displaying the Chemical elements Although precursors to this table exist its invention is Hence Todd suggested the Greek term for "at the same place" as a suitable name. Soddy adopted the term and went on to win the Nobel Prize for Chemistry in 1921 for his work on radioactive substances.

Soddy's use of the word isotope was initially with regard to radioactive (unstable) atoms. However, in 1913, as part of his exploration into the composition of canal rays, J. J. Thomson channeled a stream of ionized neon through a magnetic and an electric field and measured its deflection by placing a photographic plate in its path. Anode rays (or Canal rays) were observed in experiments by a German Scientist, Eugen Goldstein, in 1886 Sir Joseph John “JJ” Thomson, OM, FRS (18 December 1856 &ndash 30 August 1940 was a British Physicist and Nobel laureate Thomson observed two patches of light on the photographic plate (see image on right), which suggested two different parabolas of deflection. This was the first observation of different stable isotopes for an element. Thomson eventually concluded that some of the atoms in the neon gas were of higher mass than the rest.

Variation in properties between isotopes

Chemical and atomic properties

A neutral atom has the same number of electrons as protons. Thus, different isotopes of a given element all have the same number of protons and electrons and the same electronic structure, and because the chemical behavior of an atom is largely determined by its electronic structure, different isotopes exhibit nearly identical chemical behavior. The main exception to this is the kinetic isotope effect: due to their larger masses, heavier isotopes tend to react somewhat more slowly than lighter isotopes of the same element. The kinetic isotope effect ( KIE) is a variation in the Reaction rate of a Chemical reaction when an Atom in one of the reactants is replaced This is most pronounced for protium (¹H) vis-à-vis deuterium (²H), because deuterium has twice the mass of protium. A hydrogen atom is an atom of the chemical element Hydrogen. The electrically neutral Deuterium, also called heavy hydrogen, is a Stable isotope of Hydrogen with a Natural abundance in the Oceans of Earth The mass effect between deuterium and the relatively light protium also affects the behavior of their respective chemical bonds, by means of changing the center of gravity (reduced mass) of the atomic systems. Reduced mass is the "effective" Inertial mass appearing in the Two-body problem of Newtonian mechanics. However, for heavier elements, the absolute mass of nucleus relative to electrons if far more, and the relative mass difference between isotopes is much less, and thus the mass-difference effects on chemistry are usually negligible.

Isotope half lifes. Note that the darker more stable isotope region departs from the line of protons Z = neutrons N, as the element number Z becomes larger

Similarly, two molecules which differ only in the isotopic nature of their atoms (isotopologues) will have identical electronic structure and therefore almost indistinguishable physical and chemical properties (again with deuterium providing the primary exception to this rule). In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by Isotopologues are molecules that differ only in their isotopic composition The vibrational modes of a molecule are determined by its shape and by the masses of its constituent atoms. Consequently, isotopologues will have different sets of vibrational modes. Since vibrational modes allow a molecule to absorb photons of corresponding energies, isotopologues have different optical properties in the infrared range. In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of

Nuclear properties and stability

Atomic nuclei consist of protons and neutrons bound together by the strong nuclear force. In particle physics the strong interaction, or strong force, or color force, holds Quarks and Gluons together to form Protons and Because protons are positively charged, they repel each other. Neutrons, which are electrically neutral, allow some separation between the positively charged protons, reducing the electrostatic repulsion. Neutrons also stabilize the nucleus because at short ranges they attract each other and protons equally by the strong nuclear force, and this extra binding force also offsets the electrical repulsion between protons. In particle physics the strong interaction, or strong force, or color force, holds Quarks and Gluons together to form Protons and For this reason, one or more neutrons are necessary for two or more protons to be bound into a nucleus. As the number of protons increases, an increasing ratio of neutrons are needed to form a stable nucleus (see graph at right). For example, although the neutron:proton ratio of ³He is 1:2, the neutron:proton ratio of ²³⁸U is greater than 3:2. As a rule, there is, for each atomic number (each element) only a handful of stable isotopes, the average being 3. 4 stable isotopes per element which has any stable isotopes. Sixteen elements have only a single stable isotope, while the largest number of stable isotopes observed for any element is ten (for the element tin). Tin is a Chemical element with the symbol Sn (stannum and Atomic number 50

Other effects besides the bulk ratio of protons and neutrons affect nuclear stability. Of the 269 known stable nuclides, only four with both an odd number of protons and odd number of neutrons are known: ²H, ⁶Li, ¹⁰B, ¹⁴N. Also, a few long-lived radioactive odd-odd nuclides (⁴⁰K, ⁵⁰V, ¹³⁸La, ^180mTa) occur naturally. Most odd-odd nuclides are highly unstable with respect to beta decay, because the decay products are even-even, and are therefore more strongly bound, due to nuclear pairing effects. In Nuclear physics, beta decay is a type of Radioactive decay in which a Beta particle (an Electron or a Positron) is emitted In Nuclear physics, the semi-empirical mass formula ( SEMF) sometimes also called Weizsäcker's formula is a formula used to approximate the Mass

Although isotopes exhibit nearly identical electronic and chemical behavior, their nuclear behavior varies dramatically. Adding neutrons to isotopes can vary their nuclear spins and nuclear shapes, causing differences in neutron capture cross-sections and gamma spectroscopy and nuclear magnetic resonance properties. Neutron capture is a kind of Nuclear reaction in which an Atomic nucleus collides with one or more Neutrons and they merge to form a heavier nucleus Gamma spectroscopy involves the Spectroscopy of Radionuclides.

If too many or too few neutrons are present with regard to the optimum ratio, the nucleus becomes unstable and subject to certain types of nuclear decay. Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. Unstable isotopes with a non-optimal number of neutrons decay by alpha decay, beta decay, or other exotic means, such as spontaneous fission and cluster decay. Alpha decay is a type of radioactive decay in which an Atomic nucleus emits an Alpha particle (two protons and two neutrons bound together into a particle In Nuclear physics, beta decay is a type of Radioactive decay in which a Beta particle (an Electron or a Positron) is emitted Spontaneous fission (SF is a form of Radioactive decay characteristic of very heavy Isotopes and is theoretically possible for any atomic nucleus whose mass is greater Cluster decay is a type of nuclear decay in which a Radioactive Atom emits a cluster of Neutrons and Protons heavier than an Alpha particle

Occurrence in nature

Elements are composed of one or more naturally occurring isotopes, which are normally stable. Some elements have unstable (radioactive) isotopes, either because their decay is so slow that a fraction still remains since they were created (examples: uranium, potassium), or because they are continually created through cosmic radiation (tritium, carbon-14) or by decay from an isotope in the first category (radium, radon).

Only 80 elements have stable isotopes, and 16 of these have only one stable isotope. Most elements occur naturally on Earth in multiple stable isotopes, with the largest number of stable isotopes for an element being ten, for tin (element number 50). Tin is a Chemical element with the symbol Sn (stannum and Atomic number 50 There are about 94 elements found naturally on Earth (up to plutonium, element 94, inclusive), though some are detected only in very tiny amounts, such as plutonium-244. See also Isotopes of plutonium Plutonium -244 has a Halflife of 80 million years Lindsay [1] estimates that the elements which occur naturally on Earth (some only as radioisotopes) occur as 339 isotopes (nuclides) in total. Only 269 of these naturally-occurring isotopes are stable (all known stable isotopes occur naturally on Earth); the other 70 naturally-occurring isotopes are radioactive, but occur on Earth due to their relatively long half-lives, or from other means of natural production. An additional ~ 2700 radioactive isotopes not found in nature have been created in nuclear reactors and in particle accelerators. Many short-lived isotopes not found naturally on Earth have also been observed by spectroscopic analysis, being naturally created in stars or supernovae. An example is aluminum-26, which is not naturally found on Earth, but which is found in abundance on an astronomical scale.

The tabulated atomic masses of elements are averages that account for the presence of multiple isotopes with different masses. A good example is chlorine, having the composition ³⁵Cl, 75. Chlorine (ˈklɔriːn from the Greek word 'χλωρóς' ( khlôros, meaning 'pale green' is the Chemical element with Atomic number 17 and 8%, and ³⁷Cl, 24. 2%, giving an atomic mass of 35. 5. Values like this confounded scientists before the discovery of isotopes, as most light element atomic masses are close to integer multiples of hydrogen.

According to generally accepted cosmology only isotopes of hydrogen and helium, and traces of some isotopes of lithium, beryllium and boron were created at the Big Bang, while all other isotopes were synthesized later, in stars and supernovae, and in interactions between energetic particles such as cosmic rays, and previously-produced isotopes. Physical cosmology, as a branch of Astronomy, is the study of the large-scale structure of the Universe and is concerned with fundamental questions about its The Big Bang is the cosmological model of the Universe that is best supported by all lines of scientific evidence and Observation. (See nucleosynthesis for details of the various processes thought to be responsible for isotope production. Nucleosynthesis is the process of creating new atomic nuclei from preexisting Nucleons (protons and neutrons ) The respective abundances of isotopes on Earth result from the quantities formed by these processes, their spread through the galaxy, and the rates of decay for isotopes that are unstable. After the initial coalescence of the solar system, isotopes were redistributed according to mass, and the isotopic composition of elements varies slightly from planet to planet. This sometimes makes it possible to trace the origin of meteorites.

Molecular mass of isotopes

The molecular mass (M_r) of an element is determined by its nucleons. For example, Carbon-12 (¹²C) has 6 Protons and 6 Neutrons. The proton ( Greek πρῶτον / proton "first" is a Subatomic particle with an Electric charge of one positive This article is a discussion of neutrons in general For the specific case of a neutron found outside the nucleus see Free neutron. When a sample contains two isotopes the equation below is applied where M_r(1) and M_r(2) are the molecular masses of each individual isotope, and % abundance is the percentage abundance of that isotope in the sample.

Applications of isotopes

Several applications exist that capitalize on properties of the various isotopes of a given element.

Use of chemical and biological properties

• Isotope analysis is the determination of isotopic signature, the relative abundances of isotopes of a given element in a particular sample. Isotope analysis is the identification of Isotopic signature, the distribution of certain Stable isotopes and chemical elements within chemical compounds An isotopic signature (also isotopic fingerprint) is a ratio of stable or unstable Isotopes of particular elements found in an investigated material For biogenic substances in particular, significant variations of isotopes of C, N and O can occur. A biogenic substance is a substance produced by Life processes Analysis of such variations has a wide range of applications, such as the detection of adulteration of food products. ^[4] The identification of certain meteorites as having originated on Mars is based in part upon the isotopic signature of trace gases contained in them. A Mars meteorite is a Meteorite that has landed on Earth and originated from Mars. ^[5]

• Another common application is isotopic labeling, the use of unusual isotopes as tracers or markers in chemical reactions. Isotopic labeling is a technique for tracking the passage of a sample of substance through a system Normally, atoms of a given element are indistinguishable from each other. However, by using isotopes of different masses, they can be distinguished by mass spectrometry or infrared spectroscopy (see "Properties"). Mass spectrometry is an analytical technique that identifies the chemical composition of a compound or sample based on the Mass-to-charge ratio of charged particles Infrared spectroscopy (IR spectroscopy is the subset of Spectroscopy that deals with the Infrared region of the Electromagnetic spectrum. For example, in 'stable isotope labeling with amino acids in cell culture (SILAC)' stable isotopes are used to quantify proteins. SILAC (Stable isotope labelling with amino acids in cell culture is a Mass spectrometry -based technique developed to detect differences in protein abundance between two (or Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl If radioactive isotopes are used, they can be detected by the radiation they emit (this is called radioisotopic labeling).

• A technique similar to radioisotopic labelling is radiometric dating: using the known half-life of an unstable element, one can calculate the amount of time that has elapsed since a known level of isotope existed. Radiometric dating (often called radioactive dating) is a technique used to date materials usually based on a comparison between the observed abundance of a naturally occurring Half-Life (computer-game page here It's already listed in the disambiguation page The most widely known example is radiocarbon dating used to determine the age of carbonaceous materials. Radiocarbon dating is a Radiometric dating method that uses the naturally occurring Radioisotope Carbon-14 (14C to determine the age of

• Isotopic substitution can be used to determine the mechanism of a reaction via the kinetic isotope effect. The kinetic isotope effect ( KIE) is a variation in the Reaction rate of a Chemical reaction when an Atom in one of the reactants is replaced

Use of nuclear properties

• Several forms of spectroscopy rely on the unique nuclear properties of specific isotopes. For example, nuclear magnetic resonance (NMR) spectroscopy can be used only for isotopes with a nonzero nuclear spin. The most common isotopes used with NMR spectroscopy are ¹H, ²D,¹⁵N, ¹³C, and ³¹P.

• Mössbauer spectroscopy also relies on the nuclear transitions of specific isotopes, such as ⁵⁷Fe. Mössbauer spectroscopy (Mößbauer is a spectroscopic technique based on the Mössbauer effect.

• Radionuclides also have important uses. A radionuclide is an Atom with an unstable nucleus, which is a nucleus characterized by excess energy which is available to be imparted either to a newly-created Nuclear power and nuclear weapons development require relatively large quantities of specific isotopes. Nuclear power is any Nuclear technology designed to extract usable Energy from atomic nuclei via controlled Nuclear reactions A nuclear weapon is an explosive device that derives its destructive force from Nuclear reactions either fission or a combination of fission and fusion. The process of isotope separation represents a significant technological challenge, but more so with heavy elements such as uranium or plutonium, than with lighter elements such as hydrogen, lithium, carbon, nitrogen, and oxygen. Isotope separation is the process of concentrating specific Isotopes of a Chemical element by removing other isotopes for example separating Natural uranium The lighter elements are commonly separated by gas diffusion of their compounds such as CO and NO. Uranium isotopes have been separated in bulk by gas diffusion, gas centrifugation, laser ionization separation, and (in the Manhattan Project) by a type of production mass spectroscopy. The World War II Manhattan Project developed the first Nuclear weapon (atomic bomb Mass spectrometry is an analytical technique that identifies the chemical composition of a compound or sample based on the Mass-to-charge ratio of charged particles

See also

• Atom
• Table of nuclides
• Isotopomer
• List of particles
• Isotopes are nuclides having the same number of protons; compare:
  • Isotones are nuclides having the same number of neutrons. History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny A table of nuclides or chart of nuclides is a graphic in which Nuclides are drawn such that one axis represents the number of Neutrons and the Isotopomers (isotopic isomers are Isomers having the same number of each Isotopic atom but differing in their positions This is a list of the different types of particles known and hypothesized This article is about a concept in nuclear physics For biochemistry see Isotonic.
  • Isobars are nuclides having the same mass number, i. e. sum of protons plus neutrons.
  • Nuclear isomers are different excited states of the same type of nucleus. A nuclear isomer is a Metastable state of an Atomic nucleus caused by the excitation of one or more of its Nucleons A nuclear isomer occupies A transition from one isomer to another is accompanied by emission or absorption of a gamma ray, or the process of internal conversion. Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions Internal conversion is a Radioactive decay process where an excited nucleus interacts with an Electron in one of the lower electron shells causing the (Not to be confused with chemical isomers. This article is about the chemical concept For "isomerism" of atomic nuclei see Nuclear isomer. )
• Bainbridge mass spectrometer

References

External links

• Nucleonica Nuclear Science Portal
• Nucleonica Nuclear Science Wiki
• International Atomic Energy Agency
• Atomic weights of all isotopes
• Atomgewichte, Zerfallsenergien und Halbwertszeiten aller Isotope
• Chart of the Nuclides produced by the Knolls Atomic Power Laboratory $25
• Exploring the Table of the Isotopes at the LBNL
• Current isotope research and information
• Radioactive Isotopes by the CDC