From Wikipedia, the free encyclopedia.
|Name, Symbol, Number||Calcium, Ca, 20|
|Series||Alkaline earth metal|
|Group, Period, Block||2 (IIA), 4, s|
|Density, Hardness||1550 kg/m3, 1.75|
|Atomic weight||40.078 amu|
|Atomic radius (calc.)||180 (194) pm|
|Covalent radius||174 pm|
|van der Waals radius||no information|
|e- 's per energy level||2, 8, 8, 2|
|Oxidation states (Oxide)||2 (strong base)|
|Crystal structure||Cubic face centered|
|State of matter||solid (paramagnetic)|
|Melting point||1115 K (1548°F)|
|Boiling point||1757 K (2703°F)|
|Molar volume||26.20 ×1010-6 m3/mol|
|Heat of vaporization||153.6 kJ/mol|
|Heat of fusion||8.54 kJ/mol|
|Vapor pressure||254 Pa at 1112 K|
|Speed of sound||3810 m/s at 293.15 K|
|Electronegativity||1.00 (Pauling scale)|
|Specific heat capacity||0.632 J/(kg*K)|
|Electrical conductivity||29.8 106/m ohm|
|Thermal conductivity||201 W/(m*K)|
|1st ionization potential||589.8 kJ/mol|
|2nd ionization potential||1145.4 kJ/mol|
|3rd ionization potential||4912.4 kJ/mol|
|Most Stable Isotopes|
|SI units & STP are used except where noted.|
Calcium is a rather hard element that is purified by electrolysis from calcium fluoride that burns with a yellow-red flame and forms a white nitride coating when exposed to air. It reacts with water displacing hydrogen and forming calcium hydroxide.
Calcium is an important component of a healthy diet. Its minor deficit can affect bone and teeth formation. Its excess can lead to kidney stones. Vitamin D is needed to absorb calcium. Dairy products are an excellent source of calcium.
For more information about Ca in living nature see Ca (biology)
Other uses include:
- Reducing agent in the extraction of other metals such as uranium, zirconium, and thorium.
- Deoxidizer, desulfurizer, or decarburizer for various ferrous and nonferrous alloys.
- Alloying agent used in the production of aluminum, beryllium, copper, lead, and magnesium alloys.
History(Latin calx, lime) Lime was prepared and used by the Romans as early as the 1st century, but calcium was not discovered until 1808. After learning that Berzelius and Pontin prepared calcium amalgam by electrolyzing lime in mercury, Sir Humphry Davy was able to isolate the impure metal.
OccurrenceCalcium is the fifth most abundant element in the earth's crust (forming more than 3%) and is an essential part of leaves, bones, teeth, and shells. Due to its chemical reactivity with air and water, calcium is never found in nature unbound to other elements, except in living organisms where Ca2+ plays a key role in cell physiology. This metallic element is found in quantity in limestone, gypsum, and fluorite. Apatite is the fluorophosphate or chlorophosphate of calcium. Electrolysis of molten calcium chloride (CaCl2) can be used to isolate pure calcium.
Isolation (* follow):
cathode: Ca2+* + 2e- --> Ca
anode: Cl-* --> ½Cl2 (gas) + e-
CompoundsQuicklime (CaO) is used in many chemical refinery processes and is made by heating and carefully adding water to limestone. When CaO is mixed with sand it hardens into a mortar and is turned into plaster by carbon dioxide uptake. Mixed with other compounds, CaO forms an important part of Portland cement.
When water percolates through limestone or other soluble carbonate rocks, it partially disolves part of the rock and causes cave formation and characteristic stalactites and stalagmites and also forms hard water. Other important calcium compounds are nitrate, sulfide, chloride, carbide, cyanamide, and hypochlorite.
Calcium has six stable isotopes, two of which occur in nature: stable Ca-40 and radioactive Ca-41 with a half-life = 103,000 years. 97% of the element is in the form of Ca-40. Ca-40 is one of the daughter products of K-40 decay, along with Ar-40. While K-Ar dating has been used extensively in the geological sciences, the prevalence of Ca-40 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. Unlike cosmogenic isotopes that are produced in the atmosphere, Ca-41 is produced by neutron activation of Ca-40. Most of its production is in the upper meter or so of the soil column where the cosmogenic neutron flux is still sufficiently strong. Ca-41 has received much attention in stellar studies because Ca-41 decays to K-41, a critical indicator of solar-system anomalies.