Calcium is a chemical element with the 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.
An oxide is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the Earth's crust consists of oxides. Even materials considered pure elements often develop an oxide coating. For example, aluminium foil develops a thin skin of Al2O3 (called a passivation layer) that protects the foil from further corrosion.
Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Earth. It has a concentration in the Earth's crust of about one gram per kilogram. In minerals, phosphorus generally occurs as phosphate.
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.
Phosphine is a colorless, flammable, highly toxic compound with the chemical formula PH3, classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting fish, due to the presence of substituted phosphine and diphosphane. With traces of P2H4 present, PH3 is spontaneously flammable in air (pyrophoric), burning with a luminous flame. Phosphine is a highly toxic respiratory poison, and is immediately dangerous to life or health at 50 ppm. Phosphine has a trigonal pyramidal structure.
Calcium fluoride is the inorganic compound of the elements calcium and fluorine with the formula CaF2. It is a white insoluble solid. It occurs as the mineral fluorite (also called fluorspar), which is often deeply coloured owing to impurities.
Calcium peroxide or calcium dioxide is the inorganic compound with the formula CaO2. It is the peroxide (O22−) salt of Ca2+. Commercial samples can be yellowish, but the pure compound is white. It is almost insoluble in water.
In chemistry, hypochlorite is an anion with the chemical formula ClO−. It combines with a number of cations to form hypochlorite salts. Common examples include sodium hypochlorite and calcium hypochlorite. The Cl-O distance in ClO− is 1.69 Å.
Calcium nitride is the inorganic compound with the chemical formula Ca3N2. It exists in various forms (isomorphs), α-calcium nitride being more commonly encountered.
Dicalcium phosphate is the calcium phosphate with the formula CaHPO4 and its dihydrate. The "di" prefix in the common name arises because the formation of the HPO42– anion involves the removal of two protons from phosphoric acid, H3PO4. It is also known as dibasic calcium phosphate or calcium monohydrogen phosphate. Dicalcium phosphate is used as a food additive, it is found in some toothpastes as a polishing agent and is a biomaterial.
Barium peroxide is the inorganic compound with the formula BaO2. This white solid (gray when impure) is one of the most common inorganic peroxides, and it was the first peroxide compound discovered. Being an oxidizer and giving a vivid green colour upon ignition (as do all barium compounds), it finds some use in fireworks; historically, it was also used as a precursor for hydrogen peroxide.
Calcium disilicide (CaSi2) is an inorganic compound, a silicide of calcium. It is a whitish or dark grey to black solid matter with melting point 1033 °C. It is insoluble in water, but may decompose when subjected to moisture, evolving hydrogen and producing calcium hydroxide. It decomposes in hot water, and is flammable and may ignite spontaneously in air.
Thaumasite is a calcium silicate mineral, containing Si atoms in unusual octahedral configuration, with chemical formula Ca3Si(OH)6(CO3)(SO4)·12H2O, also sometimes more simply written as CaSiO3·CaCO3·CaSO4·15H2O.
Group 2 organometallic chemistry refers to the chemistry of compounds containing carbon bonded to any group 2 element. By far the most common group 2 organometallic compounds are the magnesium-containing Grignard reagents which are widely used in organic chemistry. Other organmetallic group 2 compounds are rare and are typically limited to academic interests.
Diphosphane, or diphosphine, is an inorganic compound with the chemical formula P2H4. This colourless liquid is one of several binary phosphorus hydrides. It is the impurity that typically causes samples of phosphine to ignite in air.
Calcium sulfite, or calcium sulphite, is a chemical compound, the calcium salt of sulfite with the formula CaSO3·x(H2O). Two crystalline forms are known, the hemihydrate and the tetrahydrate, respectively CaSO3·½(H2O) and CaSO3·4(H2O). All forms are white solids. It is most notable as the product of flue-gas desulfurization.
Calcium copper titanate (also abbreviated CCTO, for calcium copper titanium oxide) is an inorganic compound with the formula CaCu3Ti4O12. It is noteworthy for its extremely large dielectric constant (effective relative permittivity) of in excess of 10,000 at room temperature.
Calcium perchlorate is classified as a metal perchlorate salt with the molecular formula Ca(ClO4)2. It is an inorganic compound that is a yellow-white crystalline solid in appearance. As a strong oxidizing agent, it reacts with reducing agents when heated to generate heat and products that may be gaseous. Calcium perchlorate has been categorized as having explosive reactivity. Ca(ClO4)2 is a common chemical on the soil of planet Mars, counting for almost 1% of the Martian dust, by weight.
A sulfite sulfate is a chemical compound that contains both sulfite and sulfate anions [SO3]2− [SO4]2−. These compounds were discovered in the 1980s as calcium and rare earth element salts. Minerals in this class were later discovered. Minerals may have sulfite as an essential component, or have it substituted for another anion as in alloriite. The related ions [O3SOSO2]2− and [(O2SO)2SO2]2− may be produced in a reaction between sulfur dioxide and sulfate and exist in the solid form as tetramethyl ammonium salts. They have a significant partial pressure of sulfur dioxide.
Samarium compounds are compounds formed by the lanthanide metal samarium (Sm). In these compounds, samarium generally exhibits the +3 oxidation state, such as SmCl3, Sm(NO3)3 and Sm(C2O4)3. Compounds with samarium in the +2 oxidation state are also known, for example SmI2.
