Calcium (20Ca) has 27 isotopes, from 34Ca to 60Ca. There are five stable isotopes (40Ca, 42Ca, 43Ca, 44Ca and 46Ca), plus one isotope (48Ca) with such a long half-life that for all practical purposes it can be considered stable. The most abundant isotope, 40Ca, as well as the rare 46Ca, are theoretically unstable on energetic grounds, but their decay has not been observed. Calcium also has a cosmogenic isotope, radioactive 41Ca, which has a half-life of 102,000 years. Unlike cosmogenic isotopes that are produced in the atmosphere, 41Ca is produced by neutron activation of 40Ca. Most of its production is in the upper metre or so of the soil column, where the cosmogenic neutron flux is still sufficiently strong. 41Ca has received much attention in stellar studies because it decays to 41K, a critical indicator of solar-system anomalies. The most stable artificial radioisotopes are 45Ca with a half-life of 163 days and 47Ca with a half-life of 4.5 days. All other calcium isotopes have half-lives measured in minutes or less.
40Ca comprises about 97% of naturally occurring calcium. 40Ca is also one of the daughter products of 40K decay, along with 40Ar. While K-Ar dating has been used extensively in the geological sciences, the prevalence of 40Ca in nature has impeded its use in dating. Techniques using mass spectrometry and a double spike isotope dilution have been used for K–Ca age dating.
|Main isotopes of calcium (20Ca)|
|Standard atomic weight Ar, standard(Ca)|
isotopic mass (u)
|range of natural|
|35Ca||20||15||35.00494(21)#||25.7(2) ms||β+ (>99.9%)||35K||1/2+#|
|β+, p (<.1%)||34Ar|
|36Ca||20||16||35.99309(4)||102(2) ms||β+, p (56.8%)||35Ar||0+|
|37Ca||20||17||36.985870(24)||181.1(10) ms||β+, p (74.5%)||36Ar||(3/2+)|
|40Ca[n 4]||20||20||39.96259098(22)||Observationally Stable[n 5]||0+||0.96941(156)||0.96933–0.96947|
|41Ca||20||21||40.96227806(26)||1.02(7)×105 y||EC||41K||7/2−||Trace[n 6]|
|46Ca||20||26||45.9536926(24)||Observationally Stable[n 7]||0+||4(3)×10−5||4×10−5–4×10−5|
|β−β−[n 9][n 10]||48Ti||0+||0.00187(21)||0.00186–0.00188|
|51Ca||20||31||50.9615(1)||10.0(8) s||β− (>99.9%)||51Sc||(3/2−)#|
|β−, n (<.1%)||50Sc|
|52Ca||20||32||51.96510(75)||4.6(3) s||β− (98%)||52Sc||0+|
|β−, n (2%)||51Sc|
|53Ca||20||33||52.97005(54)#||90(15) ms||β− (70%)||53Sc||3/2−#|
|β−, n (30%)||52Sc|
|54Ca||20||34||53.97435(75)#||50# ms [>300 ns]||β−, n||53Sc||0+|
|55Ca||20||35||54.98055(75)#||30# ms [>300 ns]||β−||55Sc||5/2−#|
|56Ca||20||36||55.98557(97)#||10# ms [>300 ns]||β−||56Sc||0+|
42 (forty-two) is the natural number that succeeds 41 and precedes 43.Alkaline earth metal
The alkaline earth metals are six chemical elements in group 2 of the periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). The elements have very similar properties: they are all shiny, silvery-white, somewhat reactive metals at standard temperature and pressure.Structurally, they have in common an outer s- electron shell which is full;
that is, this orbital contains its full complement of two electrons, which these elements readily lose to form cations with charge +2, and an oxidation state of +2.All the discovered alkaline earth metals occur in nature, although radium occurs only through the decay chain of uranium and thorium and not as a primordial element. Experiments have been conducted to attempt the synthesis of element 120, the next potential member of the group, but they have all met with failure.Calcium
Calcium is a chemical element with symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to its heavier homologues strontium and barium. It is the fifth most abundant element in Earth's crust and the third most abundant metal, after iron and aluminium. The most common calcium compound on Earth is calcium carbonate, found in limestone and the fossilised remnants of early sea life; gypsum, anhydrite, fluorite, and apatite are also sources of calcium. The name derives from Latin calx "lime", which was obtained from heating limestone.
Some calcium compounds were known to the ancients, though their chemistry was unknown until the seventeenth century. Pure calcium was isolated in 1808 via electrolysis of its oxide by Humphry Davy, who named the element. Calcium compounds are widely used in many industries: in foods and pharmaceuticals for calcium supplementation, in the paper industry as bleaches, as components in cement and electrical insulators, and in the manufacture of soaps. On the other hand, the metal in pure form has few applications due to its high reactivity; still, in small quantities it is often used as an alloying component in steelmaking, and sometimes, as a calcium–lead alloy, in making automotive batteries.
Calcium is the most abundant metal and the fifth-most abundant element in the human body. As electrolytes, calcium ions play a vital role in the physiological and biochemical processes of organisms and cells: in signal transduction pathways where they act as a second messenger; in neurotransmitter release from neurons; in contraction of all muscle cell types; as cofactors in many enzymes; and in fertilization. Calcium ions outside cells are important for maintaining the potential difference across excitable cell membranes as well as proper bone formation.Calcium-48
Calcium-48 is a scarce isotope of calcium containing 20 protons and 28 neutrons. It makes up 0.187% of natural calcium by mole fraction. Although it is unusually neutron-rich for such a light nucleus, its beta decay is extremely hindered, and so the only radioactive decay pathway that it has been observed to undergo is the extremely rare process of double beta decay. Its half-life is about 6.4×1019 years, so for all practical purposes it can be treated as stable. One factor contributing to this unusual stability is that 20 and 28 are both magic numbers, making 48Ca a "doubly magic" nucleus.
Since 48Ca is both practically stable and neutron-rich, it is a valuable starting material for the production of new nuclei in particle accelerators, both by fragmentation and by fusion reactions with other nuclei, for example in the discoveries of the heaviest five elements on the periodic table, from flerovium to oganesson. Heavier nuclei generally require a greater fraction of neutrons for maximum stability, so neutron-rich starting materials are necessary.
48Ca is the lightest nucleus known to undergo double beta decay and the only one simple enough to be analyzed with the sd nuclear shell model. It also releases more energy (4.27 MeV) than any other double beta decay candidate. These properties make it an interesting probe of nuclear structure models and a promising candidate in the ongoing search for neutrinoless double beta decay.Calcium (disambiguation)
Calcium is a chemical element with symbol Ca and atomic number 20.
Calcium may also refer to:
Calcium, New York, a census-designated place in Jefferson County, New York
Calcium, Queensland, a locality in the City of Townsville, Australia
"Calcium", a song on the album Accelerator by The Future Sound of London
"Calcium", a song on the album DeadBoy by BonesDonald J. DePaolo
Donald J. DePaolo is an American professor of geochemistry in the Department of Earth and Planetary Science at the University of California, Berkeley and Associate Laboratory Director for Energy and Environmental Sciences at the Lawrence Berkeley National Laboratory.