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|
| General |
| Name, Symbol, Number | Calcium, Ca, 20 |
| Series | Alkali earth metals |
| Group, Period, Block | 2 (IIA), 4, s |
| Density, Hardness | 1550 kg/m3, 1.75 |
| Appearance | silvery white |
| Atomic Properties |
| Atomic weight | 40.078 amu |
| Atomic radius (calc.) | 180 (194) pm |
| Covalent radius | 174 pm |
| van der Waals radius | no information |
| Electron configuration | [Ar]4s2 |
| e- 's per energy level | 2, 8, 8, 2 |
| Oxidation states (Oxide) | 2 (strong base) |
| Crystal structure | Cubic face centered |
| Physical Properties |
| State of matter | solid (paramagnetic) |
| Melting point | 1115 K (1548°F) |
| Boiling point | 1757 K (2703°F) |
| Molar volume | 26.20 ×103 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 |
| Other |
| 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 |
| iso | NA | half-life | DM | DE MeV | DP |
| 40Ca | 96.941% | Ca is stable with 20 neutrons |
| 41Ca | {syn.} | 103,000y | epsilon | 0.421 | 41K |
| 42Ca | 0.647% | Ca is stable with 22 neutrons |
| 43Ca | 0.135% | Ca is stable with 23 neutrons |
| 44Ca | 2.086% | Ca is stable with 24 neutrons |
| 46Ca | 0.004% | Ca is stable with 26 neutrons |
| 48Ca | 0.187% | >6×1018y | beta- | 4.272 | 48Ti |
|
| SI units & STP are used except where noted. |
Calcium is a
chemical element in the
periodic table that has the symbol Ca and
atomic number 20.
Calcium is a soft grey
alkaline earth metal that is used as a
reducing agent in the extraction of
thorium,
zirconium and
uranium. This element is also the fifth most abundant element in the earth's crust
and is an essential element for living
organisms.
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.
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.
(
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.
Calcium 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. 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[?] (CaCl
2) can be used to isolate pure calcium.
Isolation (* follow):
cathode: Ca
2+* + 2
e- --> Ca
anode: Cl
-* --> ½Cl
2 (
gas) + e
-
Quicklime (Ca
O) 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 stalagtites[?] 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.
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