Calcium - Wikipedia. Calcium, 2. 0Ca. People have used calcium’s compounds for thousands of years – in cement, for example. Learn more about acai nutrition facts, health benefits, healthy recipes, and other fun facts to enrich your diet. This is a heat of formation table for a variety of common compounds and a summary of key points to remember when doing enthalpy calculations. Calcium hypochlorite. 7778-54-3: einecs no. General properties. Pronunciation. KAL- see- . An alkaline earth metal, calcium is a reactive pale yellow 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 Latincalx . Its compounds were known to the ancients, though their chemistry was unknown until the seventeenth century. It was isolated by Humphrey Davy in 1. While the pure metal does not have many applications due to its high reactivity, it is often used as an alloying component in small quantities in steelmaking, and calcium–lead alloys are sometimes used in automotive batteries. Calcium compounds on the other hand are very widely used in many industries: for example, they are used in foods and pharmaceuticals for calcium supplementation, in the paper industry as bleaches, in cement, in the manufacture of soaps, and as electrical insulators. Calcium is the fifth most abundant element in the human body and the most abundant metal. Calcium ions play a vital role in the physiology and biochemistry of organisms and the cell as electrolytes. They play an important role in signal transduction pathways, where they act as a second messenger, in neurotransmitter release from neurons, in contraction of all muscle cell types, and in fertilization. Many enzymes require calcium ions as a cofactor. Calcium ions outside cells are also important for maintaining the potential difference across excitable cell membranes, as well as proper bone formation. Characteristics. Classification. Calcium is a very ductile silvery metal with a pale yellow tint whose properties are very similar to the heavier elements in its group, strontium, barium, and radium. A calcium atom has twenty electrons, arranged in the electron configuration . Like the other elements placed in group 2 of the periodic table, calcium has two valence electrons in the outermost s- orbital, which are very easily lost in chemical reactions to form a dipositive ion with the stable electron configuration of a noble gas, in this case argon. Hence, calcium is almost always divalent in its compounds, which are usually ionic. Hypothetical univalent salts of calcium would be stable with respect to their elements, but not to disproportionation to the divalent salts and calcium metal, because the enthalpy of formation of MX2 is much higher than those of the hypothetical MX. This occurs because of the much greater lattice energy afforded by the more highly charged Ca. Ca+ cation. Nevertheless, there are significant differences in chemical and physical properties between beryllium and magnesium (which behave more like aluminium and zinc respectively and have some of the weaker metallic character of the post- transition metals) and the group members from calcium onwards, which traditionally led to . It crystallises in the face- centered cubic arrangement like strontium; above 4. The density of 1. While calcium is a poorer conductor of electricity than copper or aluminium by volume, it is a better conductor than both of them by mass due to its very low density. For example, calcium spontaneously reacts with water more quickly than magnesium and less quickly than strontium to produce calcium hydroxide and hydrogen gas. It also reacts with the oxygen and nitrogen in the air to form a mixture of calcium oxide and calcium nitride. In bulk, calcium is less reactive: it quickly forms a hydration coating in moist air, but below 3. In the absence of steric hindrance, smaller group 2 cations tend to form stronger complexes, but when large polydentatemacrocycles are involved the trend is reversed. Most of these compounds can only be prepared at low temperatures; bulky ligands tend to favor stability. For example, calcium dicyclopentadienyl, Ca(C5. H5)2, must be made by directly reacting calcium metal with mercurocene or cyclopentadiene itself; replacing the C5. H5 ligand with the bulkier C5(CH3)5 ligand on the other hand increases the compound's solubility, volatility, and kinetic stability. Calcium is the first element to have six naturally occurring isotopes. Although extremely neutron- rich for such a light element, 4. Ca is very stable because it is a doubly magic nucleus, having 2. Its beta decay to 4. Sc is very hindered because of the gross mismatch of nuclear spin: 4. Search the database of common compounds in chemistry and get the molecular weight of any chemical formula. Ca has zero nuclear spin, being even–even, while 4. Sc has spin 6+, so the decay is forbidden by the conservation of angular momentum. While two excited states of 4. Sc are available for decay as well, they are also forbidden due to their high spins. As a result, when 4. Ca does decay, it does so by double beta decay to 4. Ti instead, being the lightest nuclide known to undergo double beta decay. Calcium is the only element to have two primordial doubly magic isotopes. The experimental lower limits for the half- lives of 4. Limewater is the common name for a diluted solution of calcium hydroxide. Calcium hydroxide, Ca(OH) 2, is sparsely soluble in water (1.5 g/L at 25 °C). Ca and 4. 6Ca are 5. It is produced in the silicon- burning process from fusion of alpha particles and is the heaviest stable nuclide with equal proton and neutron numbers; its occurrence is also supplemented slowly by the decay of primordial. K. Adding another alpha particle would lead to unstable 4. Ti, which quickly decays via two successive electron captures to stable 4. Ca; this makes up 2. The other four natural isotopes, 4. Ca, 4. 3Ca, 4. 6Ca, and 4. Ca, are significantly rarer, each comprising less than 1% of all natural calcium. The four lighter isotopes are mainly products of the oxygen- burning and silicon- burning processes, leaving the two heavier ones to be produced via neutron- capturing processes. Ca is mostly produced in a . Ca is produced by electron capture in the r- process in type Ia supernovae, where high neutron excess and low enough entropy ensures its survival. It decays by electron capture to stable 4. K with a half- life of about a hundred thousand years. Its existence in the early Solar System as an extinct radionuclide has been inferred from excesses of 4. K: traces of 4. 1Ca also still exist today, as it is a cosmogenic nuclide, continuously reformed through neutron activation of natural 4. Ca. The isotopes lighter than 4. Ca usually undergo beta plus decay to isotopes of potassium, and those heavier than 4. Ca usually undergo beta minus decay to isotopes of scandium, although near the nuclear drip linesproton emission and neutron emission begin to be significant decay modes as well. Lighter isotopes are preferentially incorporated into these minerals, leaving the surrounding solution enriched in heavier isotopes at a magnitude of roughly 0. Mass- dependent differences in calcium isotope composition are conventionally expressed by the ratio of two isotopes (usually 4. Ca/4. 0Ca) in a sample compared to the same ratio in a standard reference material. Ca/4. 0Ca varies by about 1% among common earth materials. The climate of present- day Italy being warmer than that of Egypt, the ancient Romans instead used lime mortars made by heating limestone (Ca. CO3); the name . In his table of the elements, Lavoisier listed five . About these . It is extremely probable that barytes, which we have just now arranged with earths, is in this situation; for in many experiments it exhibits properties nearly approaching to those of metallic bodies. It is even possible that all the substances we call earths may be only metallic oxyds, irreducible by any hitherto known process. Following the work of J. Electrolysis then gave calcium–mercury and magnesium–mercury amalgams, and distilling off the mercury gave the metal. Minerals of the first type include limestone, dolomite, marble, chalk, and iceland spar; aragonite beds make up the Bahamas, the Florida Keys, and the Red Sea basins. Corals, sea shells, and pearls are mostly made up of calcium carbonate. Among the other important minerals of calcium are gypsum (Ca. SO4. Canada and France are also among the minor producers. In 2. 00. 5, about 2. United States, with about 8. In the simplest terms, uplift of mountains exposes calcium- bearing rocks to chemical weathering and releases Ca. These ions are transported to the ocean where they react with dissolved CO2 to form limestone, which in turn settles to the sea floor where it is incorporated into new rocks. Dissolved CO2, along with carbonate and bicarbonate ions, are termed . The reaction results in a net transport of one molecule of CO2 from the ocean/atmosphere into the lithosphere. The weathering of calcium from rocks thus scrubs CO2 from the ocean and atmosphere, exerting a strong long- term effect on climate. Its oxides and sulfides, once formed, give liquid lime aluminate and sulfide inclusions in steel which float out; on treatment, these inclusions disperse throughout the steel and became small and spherical, improving castability, cleanliness and general mechanical properties. Calcium is also used in maintenance- free automotive batteries, in which the use of 0. Due to the risk of expansion and cracking, aluminium is sometimes also incorporated into these alloys. These lead–calcium alloys are also used in casting, replacing lead–antimony alloys. It is also used as a reducing agent in the production of chromium, zirconium, thorium, and uranium. It can also be used to store hydrogen gas, as it reacts with hydrogen to form solid calcium hydride, from which the hydrogen can easily be re- extracted. In particular, the 1. Skulan and De. Paolo. In animals with skeletons mineralized with calcium, the calcium isotopic composition of soft tissues reflects the relative rate of formation and dissolution of skeletal mineral. In humans, changes in the calcium isotopic composition of urine have been shown to be related to changes in bone mineral balance.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. Archives
August 2017
Categories |